In-game gifts and giveaways are a time-honored tactic to keep players logging into social games on a daily basis. Zynga is taking a new tack, though, with zLotto, which isn’t tied to any one of its games.

The basic idea of zLotto is that players visit a Zynga website to play a “scratch” lotto that can give prizes for any of Zynga’s biggest games. Before playing, each person must sign up for a Zynga account with a username and associated email — a step that’s not necessary to play on Facebook.

After creating an account or signing in, the next step is to virtually scratch boxes in a grid of nine to find hidden stars. As you might expect, it’s not too difficult to get a star. We found one on our third scratch.

Once you’ve got the star, you can pick a free virtual item in one of Zynga’s games, as shown in the picture above. Of course, you have to log into the game to retrieve it.

As a cross-promotional tool, zLotto looks pretty bright. Not only does it get players to sign up for a Zynga account separate from Facebook, it also provides exposure to other Zynga properties, nets a game login, and directly tweaks our human desire to gamble.

Further, the zLotto items are mostly specific to the lotto — if you want it in-game, you either pay or play (the lotto). And to keep players coming back, there are also FrontierVille-style sets of items to gather.

Finally, players can get more tickets by asking their friends to play. Here Zynga once more avoids using Facebook as the method for communicating the invitation, instead asking players to search their email or enter emails addresses by hand.

Most serious players will probably feel motivated to use zLotto, giving Zynga one more way to collect information and contact methods that are external to Facebook — which it has already been doing since this spring.  Player blogs have covered the service several times since it launched last week, so awareness is likely already growing.