Cooperative play doesn't necessarily have to be relegated strictly to the world of hardcore combat against alien invaders or terrorist-hunting. Richard Boeser's Ibb and Obb transfers the give-and-take of co-op play to a day-glo universe where gravity pulls all things to the center -- but that zero point is the screen's equator. The game world is split into two halves, forcing players to work together to solve the gravity-based puzzles by weaving through a series of portals between the two fields. Monsters complicate matters. Like only monsters can do.