Games

Ani(mated)-Chess
an OpenGL front end for a CHESSTOOL such as gnuchess.
http://www.cs.virginia.edu/~mem5w/anichess/

BillardGL
Free OpenGL billiard game for Windows and Linux with sources under GPL licence
http://www.tobias-nopper.de/BillardGL/index-en.html

The Blue Mango Quest
3D arcade game written in C/C++ and using openGL. The goal is to extend the pacman-style gameplay. This game runs both on Linux and win32 platforms and is released under the GPL License.
http://mangoquest.sourceforge.net/index.php?lang=en

Boson
A real-time Linux strategy game for two players for KDE (Open Source, GNU GPL)
http://boson.eu.org/

BZFlag
Free multiplayer multiplatform 3D tank battle game. Irix, Linux, BSD, Windows, Mac OS X and SGI platfor
http://bzflag.sourceforge.net

Cannon Smash
A free and open source 3D ping-pong game based on OpenGL. (GNU GPL)
http://cannonsmash.sourceforge.net/

CarWorld driving simulator
Small driving simulator/demo with open source code
http://carworld.sourceforge.net/

Critical Mass
SDL/OpenGL space shoot'em up game
http://criticalmass.sourceforge.net/

3D Mines
SGI MineSweeper game in OpenGL
http://www.ai.sri.com/~reddy/3dmines

Danger from the Deep
Danger from the deep (aka dangerdeep) is a Free / Open Source World War II German submarine simulation. [Linux / Windows] (C++)
http://dangerdeep.sourceforge.net/

Doom Legacy
Port of ID Software's classic Doom game with OpenGL
http://legacy.newdoom.com/

Doomsday
Win32/Linux source port of Doom, Heretic and Hexen with OpenGL and Direct3D support for graphics, and DirectX/A3D for 3D sound effects.
http://www.doomsdayhq.com/

FooBillard
Free OpenGL billard game for linux
http://foobillard.sunsite.dk/

glChess - A 3D chess interface
An open source 3D chess interface. It uses OpenGL and GtkGLArea (from GTK+) for UNIX platform.
http://glchess.sourceforge.net/

Glest
Free 3d real time strategy project
http://www.glest.org

Kokak's Doom Page
DoomGL (OpenGL compatible port of Doom) and ZDoomGL (OpenGL port of ZDoom, an advanced Doom sourceport)
http://www.doomworld.com/doomgl/

Marathon
Microsoft's own Open Source Initiative, using the GPL'ed Marathon 2 source code, called Aleph One.
http://source.bungie.org/

OpenGL Games
An index of commercial, free, open source, and freeware OpenGL based games.
http://home.pacbell.net/freundj/openglgames/

Possible Worlds
subwar / wing Commander - style openGL accelerated 3D game that runs both under Linux and Win 9x / NT / 2k.
http://possibleworlds.sourceforge.net/

PrBoom
A Doom engine that closely emulates the original game.
http://prboom.sourceforge.net/

S3D Connector
Online game finder and ELO ladder ranking for Sea3D Windows based 3-dimensional Settlers software.
http://www.s3dconnector.net/

Tux Racer
An Open Source project in which the user takes the form of Tux (the Linux Mascot) and races downhill through alpine trails.
http://tuxracer.sourceforge.net/

Tuxedo T. Penguin: A Quest for Herring.
A free and open source 3D game, that uses OpenGL, which is staring the famous penguin Tux from Linux. (GNU GPL)
http://tuxaqfh.sourceforge.net/

The Ur-Quan Masters
Multi-platform port based on the now public-domain source-code of Star Control II.
http://sc2.sourceforge.net/

Vega Strike
Describes space simulation in which players trade and bounty hunt. Includes features, forum, manual, and downloads of beta versions
http://vegastrike.sourceforge.net/