Social game developers on Facebook have been slower this year to follow each other’s genre innovations than in previous years, but there are still some active categories that are seeing the bigger companies progressively enter. City-building games are one of those, with CrowdStar becoming the latest to release its own, called Hello City.

Previously this year we’ve seen Playdom put out Social City, which now has over 11 million players. Electronic Arts followed up by releasing its Roman-themed game My Empire three weeks ago, while Ngmoco has one on the iPhone called We Rule, with a medieval theme. But the first city building games on Facebook were built by independent developers, and some still have traction.

Hello City follows along the lines established by the earlier city builders and their spiritual predecessor, SimCity. When you enter the game you find yourself viewing a small, indeterminately 20th century town with just a few buildings. Like a farming game, your goal is to plant new structures and reap the rewards; unlike a farming game, the buildings are relatively permanent. It’s also worth noting that premium structures are purchased solely through Facebook Credits; CrowdStar has been one of Facebook’s most willing partners, first launching Happy Island with Credits as the only option last December.

CrowdStar’s defining game mechanic for Hello City seems to be choosing opening and closing times for businesses. Instead of businesses automatically running for a set period before they can be harvested for money, Hello City’s buildings require you to “open” them, which requires investing an amount of money proportionate to the amount of time you want it to stay open.

The opening time in turn influences the amount of money you finally get when it closes for the day. The business can be immediately reopened for a time period as short as five minutes or as long as two days although, of course, only after investing money back in.

But aside from that feature, which allows the city genre to mimic the farming game mechanic of crops maturing at different rates, Happy City seems like a fairly standard addition to the city building genre. That could change in the future; at the top, CrowdStar has placed a prominent notice that the game is still an alpha release.

One interesting avenue for the company to take might be mini-games. Among the starting structures is a City Hall, which has a unique feature: a game in which, three times per day, the player can navigate around their city waving hello to citizens, with a number of coins earned based on how many wave back. It’s a fun way to waste a couple minutes, and stands out from the usual routine of clicking through buildings; more such mini-games would make Hello City itself stand out.