Twimon: Gotta catch 'em all!

The premise of Twimon goes something like this: You make tweets in order to acquire and raise monsters, of which there are 60 in the game. Once you've got monsters, you can use GPS tracking on your phone to tell them to attack buildings (called outposts) in the real world close to your present location, or even search for outposts in other countries.

Since it runs on Twitter and includes all the functions of a normal Twitter client as well, naturally, Twimon has a social element to it. Players can help one another conquer outposts with their monsters.