This is a simple Java 2d api based game engine that I started in 2007. Thought I'd share it on GutHub in case anyone's interested in either using it or doing something similar.
I might update this and use it as a basis for another game.
Original blog post: http://www.kevinhooke.com/2007/10/09/basic-2d-game-engine-with-sprite-collision-detection/