BZFlag is a 3D, multiplayer, tank battle zone, capture the flag game that pits players against each other in a networked environment. It runs on Windows 95/98/NT/2000, Linux, MacOS 10.x, Irix, Solaris, and others. An OpenGL accelerator is highly recommended, but it is playable with 3D in software.
SuperTux is a side-scrolling platform game. The hero in this game is Tux the Penguin, the game's only reference to Linux. On the journey to rescue Penny, who has been kidnapped by evil Nolok, Tux faces 23 different kinds of bad guys while jumping and running through 101 beautifully-drawn levels. The soundtrack is available on last.fm and similar sites.