Odamex is a free, cross-platform, modern client-server Doom engine
0 A.D. is a free, open-source, cross-platform real-time strategy game.
A free 3d game for PC that does not limit the player. Fight,Build,Gain
mGSTEP port of the Cube game engine
FreeCS is a free-software reimplementation of Counter-Strike 1.5.
A fun realistic multiplayer free-and-open-source first-person-shooter!
C/C++ , PHP, PYTHON, 3D ENGINES, CHROME NATIVE CLIENT
A massively multiplayer tank battle game.
starrydb is game server engine
A collection of all maps and games made for the TripleA game engine
Java decentralized cross-platform network multiplayer game engine
Free strategy browsergame engine.
Your death sentence awaits...
3D FPS Digital Paintball 3 Multiplayer Online Game
Library for creating turn-based games with simultaneous moves.
Action-packed local multiplayer game
Gameserver Installer/Startscript for HL1 and HL2 Games
Open Source Virtual World and MMOG Development Platform
Mighty 34th century meka action from TeamXbow
A Dungeons & Dragons Miniature Game.
A 3D multiplayer RPG based in the world of Khoras.
Opensource serious game engine for multiplayer games
Just Another Generic Shooter