Since we’ve been on the subject of classic games getting remade as social ones, there’s one “inspired” genre that has kept popping up periodically over the past months. These are social team battling games reminiscent of the Worms franchise. The first noticeable appearance was with Playfish’s Crazy Planets, and another was Playdom’s Wild Ones. However, now, the latest Worms-like game goes to a quirky turtle-slaying game from German developer Plinga called Turtle Squad.

The company’s name may have been inspired by Zynga, but Turtle Soup is nearly a clone of Worms — if you played Worms 2, then you’ve played the core of Turtle Squad. However, for those unfamiliar with the old PC title, players control a squad of five turtles, with the objective of wiping out the enemy team. Each turtle has a set number of hit points, and using a set of bizarre weaponry (i.e. a shark missile), attempt to bring all enemies down to zero.

The player and computer-controlled opponent take turns, with each choosing which turtle to move. Using basic controls (move left, right, and jump, though eventually you get tools such as a helicopter or teleporter), they can position their character (under a time limit) on uniquely designed maps, searching for the best vantage point from which to attack. From here, the player selects a weapon and fires it, but what is interesting, however, is that power (determined by holding down the fire button), direction, and angle all play a part in attack accuracy.

You see, Turtle Squad actually has fairly decent physics, as well as directional wind. Between these two factors, it is possible to curve bazooka shells, bank shot grenades, and so on. After each match the game grants you bonuses to your income based on how accurate your shooting is, as well as your average time per shot and damage per shot (determined by accuracy and weapon choice).

This money, dubbed Turtle Coins, comes in a bit useful when purchasing new weapons and tools that are unlocked in the game’s single player campaign mode. Thankfully, the task of unlocking items isn’t too frustrating as the mode is actually fairly fun, with players advancing through a number of creative levels that have increasingly difficult enemies in terms of health, numbers, and overall AI.

Regardless, once you have unlocked a weapon, you have to actually pay to research it. This actually plays into an interesting social feature where the more friends you have playing, the less time it takes to research. Unfortunately, you can only work on one development at a time, - making said expedience prudent – but likely, that is to entice further friend invites. Luckily, you can always speed things up even more by buying the weapon immediately with the virtual currency, Plinga Stars. Oddly enough, there doesn’t seem to be anywhere to actually buy it. At least not in an intuitive or visible place.

As for other social features, there are the standard feed publications, but curiously, these are coupled with preset “Brags” that openly taunt people to challenge your turtle squad. In fact, that challenge mode is the next social feature, which allows you to battle the squad put together by your friends. Sadly, it looks to just be computer controlled, but does have some potential for synchronous multiplayer.

Of course, if you don’t wish to pick fights with your friends, you can always have them join your squad. All this really does is put their name and Facebook profile picture above the turtles on the battlefield, but if they play too, the character will be granted an added health bonus.

Aesthetically, Turtle Squad looks and sounds great. The visuals and animations, coupled with the high pitched turtle voices, make it a very amusing game to play (though it’s soothing to mute it from time to time). It’s especially entertaining to watch a defeated turtle turn into a can of soup. Unfortunately, this praise also brings up our biggest complaint.

The social elements and researching of weapons aside, the core game play is virtually identical to Worms 2. Beyond that, Worms was also known for it’s cartoon visual style and high pitched English voices. Granted, these turtles aren’t from the UK, but if someone playing were to walk to the bathroom, you could probably switch out the game for Worms and they wouldn’t notice.

In the end, Turtle Squad is a fun game, but hardly very original. Its social elements are really what saves the title from being a complete rip-off of the Worms franchise, but even they still have untapped potential. This isn’t to say that social developers should stop basing their titles on classic games, it’s just saying that perhaps they should truly be more inspirational rather than mere blueprints.

Former MySpace chief executive Chris DeWolfe has been talking to social gaming companies about a possible roll-up since last year, and now the action is starting. With financial support from Austin Ventures, he and a team of other former MySpace leaders have bought casual-social gaming company MindJolt, with some big expansions in mind.

San Francisco-based MindJolt, as our readers will note, has been on Facebook for years, and regularly appears on our weekly lists of apps that are gaining the most new users. The new plan is to make MindJolt an even bigger platform for independent casual game developers, helping them reach users and make money on Facebook and other social platforms.

As of today, MindJolt says it has more than 20 million monthly active users on the web. Although it has a web site, we count 19.5 million on its Facebook application — essentially an app that contains the games MindJolt also offers on its site — and 223,000 total users on the new MySpace version it recently launched. So, almost all of its users appear to be on Facebook. Overall, the site and these apps carry 1,300 casual games from 1,000 developers, according to the company.

Many developers have ported casual games on to Facebook, but the titles have not proven to be as popular nor as lucrative as the social games that developers have built from scratch. We’re interested to see what MindJolt specifically does to change this dynamic.

The three major initiatives it is working on now, from the press release:

• Increased monetization through major brand partnerships and virtual good offerings
• Expanding MindJolt’s global presence to all relevant websites and smart phone platforms
• Working closer with game developers to create tools for single player and multiplayer social games.

DeWolfe is starting a fascinating new follow-up act — he helped found MySpace, then lead it through its purchase by News Corp. and onwards for most of the decade. He left it last year under less than great circumstances as the company was struggling to compete with Facebook in terms of traffic and product development. However, as industry sources have related to us, he helped make a lot of people money, he has a big network of friends — and he’s a talented leader.

TechCrunch has a few more details what’s going on. Austin Ventures may have put more than $20 million into the entity, which was called Platform G until it bought MindJolt and the combined company will be called MindJolt.

The following MySpace folks will be joining DeWolfe; here they are, including their new titles and former News Corp. jobs.

• Chief Technology Officer Aber Whitcomb, former MySpace chief technology officer and also a MySpace founder
• Chief Operating Officer Colin Digiaro, former MySpace head of monetization, co-founder of News Corp.’ SlingShot Labs
• SVP of Business & Corporate Development Josh Yguado, former vice president of business development at Fox Networks Group.

MindJolt cofounder Richard Fields is staying with the company, leading product strategy. Although DeWolfe has never spoken publicly about his moves into social gaming, TechCrunch reports “DeWolfe has said that he intends to execute a roll up strategy, and the company is clearly gearing up to buy more gaming companies.”

In its latest move to expand on Facebook, Playdom has bought social game developer Offbeat Creations. Playdom raised $43 million last fall — it said it would be buying companies, at the time, and it quickly did with its purchases of Green Patch and Trippert Labs.

We’ve been expecting many acquisitions of this sort to happen in 2010. Smaller developers are facing a host of new competition, from big rivals like Playdom that have established traffic, experience, operations and revenue streams, and from traditional gaming companies. Facebook’s changes to its interface and platform policies — like the recent removal of notifications — means that most developers need to come up with new strategies, which is something smaller shops have fewer resources to do.

Offbeat Creations has 8 applications on Facebook, with the largest being dice game Super Farkle. Between its apps, the developer has nearly 1.5 million monthly active users and more than 200,000 daily active users, according to AppData.

The Bellevue, Wash. company, founded by Chia Chin Lee, Robert Reichner and Tom Fakes and its team of 12 will join Playdom’s 15-person Seattle office, the companies say. Terms of the deal were not disclosed.

Not two days ago, we looked at social developer Digital Chocolate’s social city builder, NanoTowns. At the time, it still wasn’t clear as to whether or not these SimCity-like games would be the next big social genre — social game developers are betting yes, in any case, including Playdom. Here’s a look its new title, Social City.

The game is familiar enough to anyone that has played SimCity or any of the growing number of social renditions of the classic title. Players are greeted by a cartoonish, and noseless, assistant who walks you through the basics of managing a city. Essentially, players have three things to worry about: Population, happiness, and money.

Each of these three statistics are paired with different sets of structures that you can build. For population, players build houses, apartments, and hotels, with each granting a set number of citizens. Interestingly enough, the game doesn’t just grant that one number — each building will actually grant that much population every so often. For example, every eight minutes, the smallest house will produce 10 population. Of course, it’s hard to explain why 10 people are living in a single person house and why 10 more come every eight minutes… but it’s a game, so we’ll let that one fly.

Now, in order to keep citizens, you have to make them happy. This is easy enough: players simply build what are called leisure buildings which grant X amount of happiness. This includes restaurants, stores, theaters, and even décor such as trees, flowers and statues.

Money, on the other hand is earned through factories; the number of which a user can have is limited by their population. These curious businesses can apparently make everything from potato chips to prom dresses, and for a small fee, will work on the contract for X amount of time (minutes to days) before it is shipped and a sizable income is earned.

Notice how the player is rewarded by population? This is actually one of the highlights to Social City. It seems that whenever the player makes a significant accomplishment they earn something beyond money, or purely aesthetic items. They actually earn unique buildings and rewards for both population and level — experience towards levels is earned through virtually every action the player takes. This includes, of course, cash (officially dubbed “Coins”), extra factories, special buildings for residential or leisure purposes, and even some of the virtual currency, City Bucks.

In regards to the virtual currency, it is used for a handful of buildings. These don’t really do anything special, but are merely unique (i.e. a Chocolate Shop). The primary use seems to be the actual expansion of one’s city limits. This leads to an interesting situation: players can either spend a nominal amount of virtual currency to expand, or they must have X amount of neighbors — Facebook friends who are playing — as well as a fair amount of the in-game Coins.

However, this seems to be the only significantly different usage of social features. Everything else is fairly standard, and consists of gifting, sharing accomplishments, leaderboards, and visiting each other’s cities and helping out, sort of like in the farming genre.

Aesthetically, the game looks great, and as an added bonus, players start with a respectable amount of money to get their city started and looking very nice. Most games don’t give the players enough, and it can be hard to keep them playing if they have to wait three days to make their virtual space look half decent. Social City, however, has immediate reward. Furthermore, this city actually feels alive. Sadly, there are no cars, but tiny residents actually walk about, hawk wares outside stores, mow lawns, and even work in the factories.

There is one really big complaint, though. You can’t rotate any of your buildings! It seems small, but as a game that is partially revolving around aesthetics, it looks absolutely terrible to have a house, with its back to the road. Everything faces southwest, and makes it exceedingly difficult to make things look the way they should. This is likely a technical limitation, however.

On a more minor note, it does become obnoxious to have to click on each residence to increase your population when it’s ready. Moreover, the doorbell noise it makes when ready gets very grating, very quick. Frankly, it would be better to just make it automatic and quieter (plus it keeps making the dog bark).

Overall, Social City is a fantastic game. Okay, so it isn’t SimCity, but few games are. It does have a few nits and kinks to work out, but it is still a lot of fun, with some very quick user rewards for new players. Obviously, as a new title, the monthly active user count isn‘t high yet (only around 230), but this game comes highly recommended and will most certainly boom in population, soon enough.

Gains are down a bit this week on our AppData list of top movers by growth in daily average users (DAU). Otherwise, it’s a pretty average week, with the usual mix of developers, mostly large. However, Facebook removed notifications on Monday and this could be starting to affecting traffic — we’ll be tracking the impact.

PetVille, by Zynga, leads off the list. In fact, Zynga has led both our weekly DAU and monthly average user charts for several weeks with one app or another. But it’s interesting to contrast the gains the developer’s different games are making.

FarmVille, for instance, has repeatedly lead our MAU chart with millions of new monthly users, but has yet to make an appearance for DAU gains. PetVille or Texas HoldEm, on the other hand, are doing better at adding new daily users.

Anyway, take a look at all 20:

	Name	DAU	Gain	Gain, %
1.	PetVille	5,278,982	+548,611	+10.39
2.	Zoo World	2,646,777	+528,548	+19.97
3.	Mafia Wars	6,748,137	+311,777	+4.62
4.	MindJolt Games	3,305,651	+287,834	+8.71
5.	Birthday Cards	2,092,351	+241,275	+11.53
6.	Bubble Island	244,197	+149,250	+61.12
7.	Tiki Resort	249,100	+145,846	+58.55
8.	Country Life	2,710,420	+144,347	+5.33
9.	Is Cool	666,327	+84,634	+12.70
10.	MMA Pro Fighter	87,696	+60,729	+69.25
11.	Glamble	74,612	+57,290	+76.78
12.	Happy Island	3,226,107	+55,365	+1.72
13.	How Fast Are You?! PROVE IT	203,019	+48,025	+23.66
14.	Hug Me	244,074	+46,319	+18.98
15.	Friends For Sale!	574,131	+44,041	+7.67
16.	Texas HoldEm Poker	6,177,174	+42,201	+0.68
17.	Music Pets	50,445	+39,209	+77.73
18.	開心寶貝	613,094	+26,146	+4.26
19.	Kingdoms of Camelot	228,247	+25,584	+11.21
20.	Farkle 2	125,245	+24,241	+19.35

RockYou has jumped back onto this week’s list with Zoo World and Birthday Cards. The two seemed ready to take up permanent residence about a month ago, but then backslid a bit. Their gains this week are actually a recovery from an earlier dip.

While we’re pointing out big developers with uneven DAU growth, we’ll take time to mention one that’s not listed above at all: Slide. One would think that after Slide’s meteoric growth in monthly users it would also appear here, but its games — including SuperPoke! Pets, SPP Ranch! and Top Fish — haven’t been converting many monthly users to daily ones.

MindJolt Games, the catalogue of a few hundred mini-games, is yet another big app, but in its case the news is all good: both its MAU and DAU are up.

The news is also pleasant for Tiki Resort, the new island building app from Playdom, and Happy Island, by CrowdStar. The latter has been out longer, and its percentage gains are pretty slim, but it has showed up reliably for several weeks.

We’ll close out with two more apps: MMA Pro Fighter from Digital Chocolate, and Glamble. The first is an older mixed martial arts fighting RPG that never grew much, the second a new Texas Hold’em game. At the rate both are taking off now, it looks like we’ll get to see them again on our Friday list of emerging games; but even if they don’t make an appearance there, they’re probably worth keeping an eye on.

A few month ago, we first wrote about the trend of fan blogs appearing for Facebook games like FarmVille and Pet Society. Avid gamers have been creating professional-looking sites that both provide a community for supposedly “casual” gamers, and share news on in-game changes and fresh strategies.

As a new trend, fan blogs still have an uncertain future; some have grown fairly quickly, while others, including most that we mentioned back in October, haven’t grown at all. We spent some time looking for the more successful blogs. Four are shown below on a Compete graph:

Keep in mind that Compete isn’t always accurate — it quite often underestimates traffic to small sites. Worse, it only counts traffic in the United States, whereas Facebook games are an international trend. Traffic to these English-language sites is probably significantly higher than reported, and there are also quite a few foreign-language blogs around.

One simple way to track this larger audience is to head over to Google Trends and search for terms like FarmVille and Facebook cheats.  In many cases, the United States isn’t even in the top five for search term growth, being outweighed by countries like the Phillipines and Turkey.

Another thing to note is that the number of blogs following any given game isn’t proportional to the number of players it has. Café World, for instance, is the second-largest game on Facebook, but doesn’t have a large blog following. Generally speaking, the games most successful in creating vocal fan followings are those that are highly competitive, like Mobsters, or that involve difficult to obtain in-game virtual goods, like FarmVille.

You can see FarmVille’s outsized influence above, through the growth of FarmVille Freak. This blog is definitely an outlier in terms of growth. It’s also at the forefront in its design. The top banner shows off the blog’s visual chops, while the stories are short and to the point, with a good mix of news, feature reviews and hints on how to get ahead.

That’s not all there is to the site, either. There’s also a chat room, FAQ, forum and gallery — the site is actually quite large. In some ways, FV Freak is beginning to resemble the much larger dedicated sites that MMORPGs like World of Warcraft have inspired.

This growth of gaming blogs into multi-faceted communities, with different activities for a range of players, may be the direct result of the growing complexity of games like FarmVille. Web gaming has always had large sites like Kongregate and MSN Games that double as gaming portals and community sites, but websites following particular games are rare.

For Facebook’s games, that’s changing. Check out Pablo Paniagua’s blog for an example of how; Panaguia has written two posts in a row breaking down the economics of planting different trees and raising various animals on FarmVille.

The question is whether Facebook game blogs can catch up with the huge user communities spun out by MMORPGs. On the one hand, the idea sounds ridiculous; WoW’s players are clearly far more engaged than the average social game player, and the game world is much larger.

But when WoW got started, it wasn’t taken for granted that huge, independent player communities would spin out of the game. Three years ago I interviewed Hubert Thieblot, the young French founder of a WoW community site called Curse.com.

At the time, Curse was still settling into its swanky new San Francisco offices. Employees lined a long table in the main room, while Thieblot sat in an office, looking vaguely uncomfortable. He had good reason to feel out of place; another two years before, in 2005, Thieblot had just been another addicted teenage WoW player. The explosion of users on his site, a side project, brought revenue, employees and soon, venture capitalists.

That clearly hasn’t happened yet for FarmVille Freak, or any other Facebook gaming site. But the possibility is evident if, rather than comparing WoW and Facebook games by their game worlds, we look at game mechanics and addiction. As we’ve covered before, there are clearly at least sone addicted Facebook gamers.

According to WoW statistics, the average user spends 22.7 hours per week playing the game. Contrast that with a recent PopCap study, which showed that only 12 percent of social gamers are addicted enough spend 10 or more hours per week gaming. But WoW has about 12 million players, while FarmVille alone has 83 million monthly active users. So could a Facebook game community explode? You do the math.

In a clear bid for Facebook’s momentum as a social gaming platform, Hi5 is expanding its developer platform beyond OpenSocial, implementing a substantial portion of the Facebook Platform APIs on Hi5. This will allow companies with Facebook apps — especially social gaming companies who have figured out how to get a lot of users — to more easily port their applications without having to rewrite much code.

Friendster and Bebo have supported parts of the Facebook Platform API for years, but they have not always maintained support for changing Facebook Platform API specs, which often decreases the ultimate efficiency gains for developers. In addition they have not been as focused on building social games, as Hi5 has been for the past year, rolling out its virtual currency, flash games, avatars, chat, a redesign, and more. From the company on today’s news:

hi5’s Facebook compatible interfaces, which are currently in use by select partners, support the functionality needed by most social media games to add social elements to their applications, including user authentication, profile pictures, friends, updates and photos. The new APIs also support the JavaScript interfaces necessary to enable user actions such as friend invitations.

We’re still waiting on details from Hi5 on the exact API documentation. Hi5 says it is “starting with the REST-based server-side APIs, as well as several JavaScript APIs.”

Attracting established social gaming developers could make Hi5 more popular with users. Facebook’s many changes — like the removal of notifications that allowed for many apps’ viral growth — have gotten developers increasingly eying other platforms. But while Facebook has grown to more than 400 million monthly active users, most in the last year, Hi5 has stayed level at what it says is 50 million total users.

Hi5 is continuing to make the right moves given its position, specializing in gaming while Facebook stays focused on being an all-purpose social service. It’s hire of Alex St. John, a gaming pioneer, and the recent mostly-talent purchase of veteran game and virtual goods developers at Big Six show its focus on continuing to build in gaming.

Now, the company needs to tie all of its pieces together in a way that resonates with users, like Facebook’s focus on real-world identity and its news feed have. Hi5 is in a fascinating position, and we’re intrigued to see how it continues to mold its service and improve social gaming.

The company will be providing more details on the platform later this month, although St. John tells VentureBeat that he wants companies with new games, hoping to get them launching those games on both sites.

Hi5 says it has developer partners lined up. It isn’t naming them yet aside from Detonator Games, a new company recently started by former Sony Online Entertainment employees; Hi5 has previously had deals with other companies, including RockYou and Playdom.

Hi5 promises more news to come: “This effort is the first of many new technologies we will be announcing over the coming months to make hi5 the leading marketplace for great social media games.”

The Christmas traffic decline has melted away, and a number of games saw significant growth in February — more so than January, anyway. However, for each significant gain, there were some loses as well, as roughly one-third of the list dropped in monthly active users, and a few of those drops are highly popular titles such as FishVille and Happy Aquarium.

On the lighter side of things, Zynga’s FarmVille continues to hold on to top honors with new records in monthly users once again, while competitor CrowdStar attempts to increase its popularity even further. Also, RockYou makes its move back to its former glory from the early days of Facebook with heavily increased MAUs for both Birthday Cards and Zoo World. Another game, Hero World, also made its debut this month.

February was a potentially big month for games, because Facebook introduced a home page redesign at the beginning of the month that moved applications from a bottom toolbar into the left-hand navigation column, and moved notifications from the toolbar to the top navigation bar. Facebook also added what it calls a Games Dashboard — basically, a home page filter that lets users see a page of the Facebook games they and their friends have been playing. So far, the impact does not look to be negative for social games overall. The full impact of the redesign will only be felt this month, though, as Facebook is removing application notifications from the new notifications bar.

Here are the highlights for the top 25 Facebook Games for February, 2010:

• Zynga‘s FarmVille shatters its old records once again, gaining over 7.5 million new monthly active users, bringing the game’s total monthly players up to a whopping 83,004,461.
• At a distant second comes RockYou‘s Birthday Cards with just over 47 million MAUs, having gained over 7 million new users as well — this gift-giving app isn’t really a game, although it contains a virtual currency. Rather, it has included a window for RockYou’s game Zoo World (more on that in a moment).
• Surprisingly, the virtual aquarium games did not do too well through February as Happy Aquarium from CrowdStar lost over 1.5 million users, with Texas Hold’Em Poker moving past it to #4. Zynga’s FishVille also dropped from #5 to #7 with roughly a 850,000 MAU loss. Furthermore, Fish World, from Tall Tree Games, has completely fallen off the charts.
• Though aquariums aren’t doing too well, zoo keeping seems to be growing as RockYou’s Zoo World gains an impressive 4.1 million monthly active users, showing that simple mechanics and cute animals — and however else the app is growing — can go quite far. It comes in at #8, up from #10.
• After a long game of cat and mouse, Playfish‘s Pet Society finally loses out to PetVille by a difference of less than 300,000 users. They come in at #10 and #9 respectively.
• While CrowdStar’s long popular fish game dropped, the cold winter nights have proven lucrative for its tropical Happy Island app, as this warming title moves up from  #17 to #14 with almost a 2 million MAU gain. Unfortunately, Happy Pets still staggered slightly, losing 566,909 users, and dropping one ranking, to #17.
• In regards to tropical games, Island Paradise, from Meteor Games also sees minor growth, moving up one rank to #19, with just over 7.6 million monthly active users, and just behind it comes RockYou’s Hero World. The super hero RPG earns 7,033,749 MAUs for the month of February.
• Little farming app (Lil) Farm Life reappears on the list, coming in with about 5.9 million MAUs and landing at #22.
• Lastly, the boom that was Shikha’s Pillow Fight seems to have died out, as the app has lost more than 8.4 million users, dropping from #14 to #25.

While drastic fluctuations in users have never been the mark of MySpace applications, the coming core changes to the social network – including analytics – might provide some better insight into the site. MySpace applications may not be as big as Facebook’s, but developers have often reported higher revenue from them.

Nevertheless, the current method of tracking still showed some minor changes over January’s charts, with almost no games earning a negative monthly change. Of course, that doesn’t mean that a handful of titles didn’t shift about in February. In fact, even a newcomer appeared at the tail end of this month’s list.

On another note, many games on the MySpace list can often be classified as merely fun applications as opposed to “games” by traditional definitions. We track some of these applications because they have significant social game-like features.

Here are the highlights for the Top 25 MySpace Games for February, 2010:

• Unsurprisingly, the two mafia role playing games of Playdom‘s Mobsters and Zynga‘s Mafia Wars appear at #1 and #2 respectively. The two titles earn over 14.4 and 13.1 million installations.
• The simple concepts of Bumper Stickers and Own Your Friends from Playdom, continue to show that simplicity is the predominant preference for users on MySpace as each earn over 12.5 and 10.2 million installs.
• Another simple app, Tag Me from BitRhymes moves up from #9 to #8 to pass RockYou‘s Super Pets (now dubbed RockYou Pets in the app gallery), with almost a 500,00 installation gain.
• BitRhymes app, Cheers!! also moves up one ranking to #10 to beat out the Zynga RPG, Vampires. It earns just shy of 5 million installs, but again, does not appear in the app gallery. More likely than not, this issue, that we have noted numerous times, is almost certainly hindering its growth.
• Same as January, Playdom controls ranks #13-#16 with Kiss Me (4,059,001), Sorority Life (3,566,896), Poker Palace (3,386,269), and Overdrive (2,626,783).
• Another simple app from Oxylabs Networks, PhotoBuzz sees an impressive jump, moving up from #23 to #21 with a gain of 152,316 new users. It now totals over 1.9 million installations.
• In fact, newly added to the list is another app from Oxylabs, What is your Street Reputation, which garners over 1.7 million installs. The game appears at #24 ousting Green Spot form the Top 25 and was added due to its similarity to What’s my Impression on friends from BitRhymes.

We’ve been talking a lot about Slide recently, and for good reason. After staying pretty flat for months at around 20 million monthly active users, Slide’s growth started to explode a few weeks ago. Since February 14th, the company has doubled its MAU to almost 40 million, of whom over five million are daily active users.

What happened? A combination of Facebook’s redesign, plus some cross-promotion, a little advertising, and the clever use of viral features. We talked with Keith Rabois, Slide’s vice president of business development and strategy, to get some background.

FunSpace has grown the most since mid-February. On the 16th, it was still at 4.5 million MAU; today it accounts for about half of Slide’s MAU, at 21.7 million MAU. It is focused on sharing videos and other content. This is generally what Facebook wants to enable, and its own data reflects the trend.

Our regular readers will notice that around two weeks elapsed between Facebook’s design changes in early February and the explosion in growth for FunSpace. This is where Slide’s viral tactic comes in, a method Rabois describes as letting users share videos with a lot of friends in a way that follows Facebook’s developer policies.

Besides FunSpace, most of Slide’s other apps also involve content sharing, of sorts, and this may be helping them grow, too.

Cute mammal-caring games like SuperPoke! Pets, SPP Ranch! and SuperPocus, and aquarium game Top Fish are more virtual worlds than games. Slide began testing out virtual marketplaces in some of these apps in January, letting users create their own virtual goods, sell them and make money, similar to aspects of virtual worlds like Second Life and IMVU.

In January, Rabois says that users made $160,000 on their creations. To expand the model, Slide will need to manage fraud and provide creation tools but the results so far suggest that the effort would be worth it. The company already offers virtual goods creation tools, the marketplace and ecosystem features designed for user-created goods, like a method for selecting the best user creations and promoting a limited number to other users. So far, so good — we’ll be watching to see if other application developers adopt similar virtual goods marketplace.

While none of the apps are seeing nearly as much growth as FunSpace, they are all growing — partly due to cross-promotion from FunSpace, it seems. Still, SPP Ranch!’s traffic was already on the way up, according to AppData. Slide doesn’t spend much on advertising, so on top of the other reasons mentioned, the virtual goods marketplace — and the profusion of additional goods that players are getting access to — could be playing a role in drawing making the apps more popular.

Overall, Slide’s combination of content-sharing apps and virtual world-style games seems to be helping it gain more users, and monetize them. Having been one of the largest developers on Facebook since the platform launched in 2007, its reach, experience and funding — and its range of growing apps — put it in a promising position to build its business.