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.
pydance is a dancing game written in Python, formerly named pyDDR. The idea is simple. There's a floor mat with arrows, and the game scrolls arrows up the screen to the beat while playing a song. When the arrows reach the top of the screen (not sooner and not later), the player hits the corresponding arrow on the pad, and given that it's hit on time with the beat, points are scored. Based on how well the dance is put together, s/he is graded at the end of the song. Both keyboard and mat play are supported.
This project is a collection of robots for the robocode framework. Robocode is an alphaworks project from IBM that provides an environment for creating software robots that compete against each other. This collection provides examples for people who wish to write their own robots.
XPilot is a graphical multi-player maneuvering game with less-exciting graphics, but more speed, tactics, and insults. Some people also use it for UDP network analysis. Over the past eight years of playing and development, tons of features have been added to the game, from basic weapons like shotguns and missiles to more recent ones like phasing devices, invisibility, or hyperjump.
Free Tennis is a tennis simulation developed by a former tennis player. Its main feature is realism. For gameplay, "realism" means you have total control over the shot parabola. For graphics, it means players have realistic gestures. For AI, it means real tactics. A two-player mode via LAN is available.