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)
Underworld is a massive multiplayer online role playing game (MMORPG) based on web technologies, so it can be played with any web browser. It is a fantasy game in which the player can be either a human or a monster: combats, spells, buy/sell items