ZDoom is an enhanced port of the official DOOM source. It features support for all Hexen editing features (including ACS, hubs, etc.), support for most BOOM editing features, freelook, jumping, and translucency support, a Quake-style console, high screen resolutions, removal of the original DOOM's limits, support for many more music formats (including MOD, IT, XM, S3M, MIDI, MP3, and MUS), better mouse support, UDP networking, and more.
Adanaxis is an action game where the fundamentals of space itself are changed by adding a fourth dimension to space. Initially, it's like learning to play a 3D FPS for the first time, as the hand and eye have to learn a whole new type of coordination. The gameplay involves rapidly blowing things out of the sky, with the usual assortment of enemies, allies, weapons, and power-ups, together with commercially sourced graphics, audio, and voice acting.
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.
Alpha Shooter is a 3D first-person shooter game with a sci-fi setting. It features multi-platform support (Linux, Mac OS X, CygWin, and Windows) and, since version 0.1.0, its own reusable game engine (Neutron). The game and its engine will evolve over time to incorporate simulated physics and AI, networking, audio, scripting, and more.
Crystal Core is a FPS quest-based game written with Crystal Space and Crystal Entity Layer. The game is based on a science fiction story. The player and his or her companions crash on an alien planet where they discover that the original intelligent inhabitants are now extinct due to an invasion of semi- primitive aliens from a distant planet. Your goal is either to destroy all aliens or escape the planet alive. To accomplish these goals you have to use alien technology and try to interface it with the broken ship that you arrived with.
EDM is a fork of Sauerbraten (http://www.sauerbraten.org/) which is in development but playable. It features several multiplayer game modes like Deathmatch and Instagib, dynamic map model physics, enhanced particle effects, unique weapons and powerups, and more. Maps can be edited with other players online.