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.
0verkill is a client-server 2D deathmatch-like game in ASCII art. It supports free connecting/disconnecting during the game, and runs well on modem lines. Graphics are in 16-color ASCII art with elaborate hero animations. 0verkill features 4 different weapons, grenades, invisibility, and armor. The package also contains reaperbot clients, a simple graphics editor, and a level editor.
Nexuiz is a fast-paced, chaotic, and intense multiplayer first-person shooter game, focused on providing basic, old style deathmatch. It is extremely modder-friendly. Nexuiz is built on the power of the Darkplaces engine, which is a heavily modified version of the original Quake. Darkplaces features realtime lighting and stencil shadows, bumpmapping, gloss, bloom, and totally rewritten network code that supports up to 64 players on a single server.
The Interreality project is a collection of Open Source, Free Software projects based on the Virtual Object System (VOS) platform. The goal is to develop a free and open platform for multi-user 3D virtual reality games, applications, and interactive, collaborative 3D virtual spaces. VOS is a powerful and generic network object framework designed to support a variety of high-performance applications. It is the basis for Ter'Angreal, a general-purpose browser application for entering and participating in 3D worlds.
Doom was the classic 3D shoot'em'up game from id Software. PrBoom is a game engine for playing Doom levels, which runs on both Windows and Linux/Unix systems. It uses the SDL graphics library. PrBoom a very faithful Doom port, with great effort taken to be compatible with as many original Doom levels and demos as possible.
DooM Legacy is an enhanced port of Doom, the classic first-person shooter from iD Software. It features high screen resolutions, an OpenGL renderer, fullscreen modes under X, client-server architecture for up to 32 players on IP-networks, Quake-style keybindings, a console, and more. It is available for Linux, DOS, and Win32.
UProxy is a proxy for UDP protocols. UProxy was initially designed to allow users to play Unreal Tournament matches over the Internet on computers sharing a dial up connection. It could also be used by any client-server application that uses the UDP protocol and doesn't require clients to bind a fixed port. UProxy should run under Windows, Linux, or any OS which supports BSD sockets.
Vavoom is a DOOM source port incorporating Doom, Heretic, Hexen, and a little bit of Quake. It runs on DOS, Windows, and Linux and includes many advanced features like OpenGL and Direct3D support, translucency, freelook, jumping, a client/server architecture with in-game joining, a Quake-style console, a powerful language to describe game logic (Vavoom C), and much more.