Source of Mana is a unique 2D MMORPG
Combat Flight Simulator for LINUX. WW2. Network and VOIP. Open-source.
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
Crossfire RPG Game Weather Patch -- Now a branch on the official repo!
Alternative Teeworlds Client with many exciting features!
Free MMORPG
JAVA websocket implementation for a bomberman-like game
Star Trek Web browser game
Advanced Wasteland mission using ACE for Arma II
The original Xivio.com World Server Core
Wizard of wor HTML5 remake.
Open Source Virtual World and MMOG Development Platform
Modular Minecraft server plugin - commands, events, ...
A lame multi-user dungeon engine.
Space Exploration Game
Multi-user whiteboard emphasizing simplicity.