Desktop/Android/HTML5/iOS Java game development framework
Arianne is an engine to develop multiplayer online games like Stendhal
A simple cross-platform game engine for creating old-school 2D games
Java Settlers
8-bit Graphical API for Java
Source code of the chapters of the book 3D Game Development with LWJGL
Example code for creating a 2D platform game in Java.
MultiLingual Interactive Fiction
Open Source Virtual World and MMOG Development Platform
AMOS BASIC reimplementation in Java
Modular Game Creation Framework.
The next generation mud is an open-source extensible, programmable mud
Utility math library for develping 2d games