Dungeon Defenders by trendy games
Great cross platform game.
I got this game about a year ago, at the time it was available for android and iphone. Now I just discovered it is not available at google play, but I am sure you can find a download somewhere (it is a free app, no paid versions for mobile).
This is a tower defense/ rpg game. I don't like tower defense games in general but I really like this game.
Now that I've been playing it for a year, they have come out with PS3, X-box, and PC versions of this game, so I think it is truly cross-platform.
I haven't had time to play the PS3 or PC version yet so I'm not sure if you can import your characters or if you have to start over from scratch