Free MMORPG Engine. Develop and host graphical browser-based games.
DimensioneX is a free Massive Multiplayer Game Engine.
It lets you develop and then run or host browser-based, graphical multiplayer games. The users will play games simply via their browser.
DimensioneX runs on any Java-enabled web server (eg. Tomcat)
A distributed system for interactive games. Specifically, RoD is designed with the RPG/Adventure style games in mind but could easily be used for other kinds of interactive games.