FreeTribes is an empire building, highly strategic MMORPG. The game in its entireity is being completely re-written from scratch, under GPL and will use Python and PHP. More information at http://www.phplogix.com/wiki/
OCGP is a free game online writing in Php. The project was launched in January 2008 and one version alpha should leave for December 2008. OCGP is a MMORPG of strategy and management in an underwater environment. Playing with a simply web browser.
Hallow[Online] is an open source 2D MMORPG written in C# using the following wrappers: Irrlicht.NET (rendering), irrKlang.NET (sound/not open source), MySQL Connector, and various libraries that are packaged with the .NET framework!
A web-based game in the spirit of Archmage of a post-apocalyptic future. A jsp-based MMORPG where users control empires spanning many worlds. Writers and artists welcome. Employing Struts MVC, Tomcat, mySQL, and Java. Knowledge of design patterns helpful
RangelOnline is a MMORPG done in PHP. He is a Web game simple, but fun. Its goal is winning the other players and dominate the world "Rangel."
Knights of War is an open-source massively multi-player online role-playing game (MMORPG)
OpenTravia is a open source clone of Travian game.
Syndron is a futuristic (turn-based like) MMORPG game. Unlike other online strategy games this one is not a browser game but a real client-server application designed for thousands of players. This is the client app. written in C++ / QT-GPL. License: GPL