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.
"The Game" is a project designed to simplify the process of producing any high-quality cross-platform 2D or 3D graphical computer game. The hope is that any game can be produced simply by changing a few settings and pressing a "compile" button. The project has three "deliverables": a game engine library to abstract across the set of all possible computer games (applying object-oriented design methods to the general problem in such a way as to be usable in specific instances); a graphical interface for easy game design (an exercise in human interface design); and a gaming package with a lot of shiny games to play.
Tremulous is a computer game that blends a team-based first-person shooter with elements of realtime strategy. The objective of the game is to annihilate the opposing team. This is achieved by eliminating the opposing players and removing their ability to respawn by destroying their spawn structures.