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 tactics RPG engine written in almost entirely in javascript (only a java applet for music/audio). Allows creation of tile based RPGs with javascript events and commands, and should work in most javascript capable browsers.