A browser game framework implemented with Grails. The goal of Little Goblin is to create a game engine that allows you to "just add content" and you will be able to host a game that is only limited by your creativity.
JGachine (Java Game machine) is a networked game engine for 2D multi-player (networked) games. JGachine is written in Java and C++. The games themselves are written in pure Java and can be loaded via network. (JGachine as game browser)
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)