Free first person shooter based on the game Cube
AssaultCube is a total conversion of Wouter van Oortmerssen´s FPS called Cube. AssaultCube encourages players from all platforms to play by being multi-platform (Available on: Windows, Linux and Mac OS X), partially open-source and low on system and networking requirements. It is set in a realistic looking environment (as best that's possible with this engine) while gameplay stays fast and arcade. This game is all about team oriented, multi-player fun.