BMTron - Multi-player tron light cycles game for 1-4 players with teamplay mode. (Java) [GPL] - http://kryshen.pp.ru/games/bmtron.html
SpyWar - SpyWar is an online strategic game in development phase. (PHP, PostgreSQL) [Linux] [GPL] {status: halted} - http://spywar.sourceforge.net/
Merchant Empires - Multiplayer game of space exploration and economic competition. - http://www.advancedpowers.com/
Quantum Star: Generations - A space strategy game involving Mining, Combat, Exploration, Planets and Clans played in real time. (PHP/SQL) [AGPL] - http://www.quantum-star.com/
phpRPG - A multiplayer fantasy roleplaying game driven by PHP and MySQL, with aims to develop a web-based game engine which shares common qualities between multiple user dungeons (MUDs), paper & pen RPGs and computer RPGs. [GPL] - http://phprpg.org
Blacknova Traders - Multi-player space exploration and strategy game (PHP) [GPL]. - http://www.blacknova.net/
Legend of the Green Dragon - A remake of the classic BBS Door game, Legend of the Red Dragon (aka LoRD) by Seth Able Robinson. It is written in PHP, using a MySQL backend, the game's source code is licensed under the GNU GPL. - http://www.lotgd.net