Finnish developers FrozenByte's upcoming adventure fantasy game, Trine 2, is cross-platform compatible thanks to the Steamworks platform. This basically means that Mac users can play with PC users and vice versa. Unfortunately, PS3 gamers and Xbox 360 owners won't be able to share multiplayer experiences in the new fantasy title.
Rochard is a very fun and challenging puzzle-platformer that shouldn't be overlooked. It's not often you find puzzles designed with such consistent quality and challenge.