Xiabween is a free and open source 2D game. For more information about Xiabween, you can visit my development journal, http://xiabween.blogspot.com/.
It is abandoned and unfinished (functioning more like a prototype), but it demonstrates draw ordering, collision detection, game design, and libGDX use.
Xiabween is made in Java using the libGDX game engine.
The primary source code is located in core/src.