The linux port of world of goo supported multiplayer via two mice. It was a bit of an involved setup(special udev rules if I remember correctly) but I thought i

The linux port of world of goo supported multiplayer via two mice. It was a bit of an involved setup(special udev rules if I remember correctly) but I thought it neat they took the time to make it happen. update: I looked it up. you had to change the game config and change permissions on the mouse device. so not that bad considering.