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.
Lincity is an SVGALIB (Linux only) and X based city/country simulation game for Linux and other Unix platforms (Solaris, FreeBSD, HP_UX, AIX, SCO and IRIX). There is also a Win32 version (win95 and NT) available as a separate package. The game reminds a bit of SimCity but has it's own goals and methods to get there.
Tow Bowl Tactics is a game based on Games Workshop's Blood Bowl. It is an epic conflict between two teams of heavily-armed and quite insane warriors. Players pass, throw, or run with the ball, attempting to get it to the End Zone at the end of the field to score a touchdown. Games are full of violence and carnage and could be compared to a combination of Warhammer, American football, and rugby.