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)
clanfx is a 2D, tile-based Javascript game engine developed using Javascript and CSS. It currently works in Firefox, Epiphany and Opera browsers. Features include many animated sprites, spell effects, buildings, tiles/textures and basic game AI.