A game engine in java for 2D strategy games
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. Think of it as Robocode, but then with a far more serious implementation of CGFs and AI.
I do not think you will use this engine as a whole (eg it uses AWT for visualising), but there might be parts you can reuse or learn from when building your own (strategy) game.