If you want to play with friends on the same device, check out this collection of the best one device multiplayer games. You don't need to use two devices, just play together on the same device and have a great time. Multiplayer in a different, more enjoyable way.
Apps available in other platforms:
Hexologic: "Puzzle for math addicts"
Hexologic has everything that is needed to be considered a puzzle game: there's something "broken" on your screen and you must tap everything until you can fix it. Thus, it's a game (of course it is) but is also a kind of mental trainer. I mean…