IGM2E - Individual Game Modifiable 2 Engine / Individual Game Engine
IGM2E is a simple to use, but yet powerfull and still in-developement game engine written in JAVA using Slick2D and LWJGL. It aims for being customizable, stable, open-source and usable on Windows, Mac OSX and Linux (Solaris, too!).
To use it, just start jumping around in the code and modify it to your benefits. A test map is already given here for testing some main features like map-loading.