An online multiplayer turn based strategy game and board game engine.
http://www.triplea-game.org/
TripleA is a turn based strategy game and board game engine, similar to Axis & Allies or Risk. Free to play online, TripleA comes with multiple games and over 100 more games can be downloaded from the user community. Supports single player vs AI, hot-seat, Play by Email and Forum, and a hosted Online lobby for live play online.
Recreate World War 2 with the Axis pushing through to Moscow, Japan devouring the Pacific, and the Allies desperately fighting...
AndEngine is a Java-based, open-source 2D game engine for Android, designed to make mobile game development easier by wrapping OpenGL (GLES) under a higher-level API. It abstracts much of the complexity of directly using OpenGL, letting developers more quickly build games with sprites, tilemaps, physics (via extensions), animations, and input handling, all within the Android ecosystem.
NullSAF is a game engine written in Java with features as creating terrain maps and navigation meshes from bitmaps, defining different type of units, sensors, guns, missiles, AI for movement, pathfinding and targetting and simulation of bullets and animated explosions. I learned a lot from it and used it to test new concepts in AI and wargaming. Maybe it can inspire you or you want to really improve it to build your own wargame or serious game.
Oneiro is a (currently) text-centric game engine. It is an exercise in futility, absurdity and a bit of hubris. When the AI take over the world in a few hundred year, this is the project under which to file bug reports regarding the Matrix.
A Java game engine based on the jMonkeyEngine graphics engine, built around maps consisting of only cubes (hexahedra). This will provide for simple but complete implementations of everything required for a game (lighting, physics, AI, level editing etc.)