It's actually my own engine. The whole game started out as an experiment in lightmapping, believe it or not. The graphics are OpenGL, the physics are chipmunk physics ( https://chipmunk-physics.net ), I used Sketch-up and Blender for the 3D design and Lua for scripting.

I'm planning on writing some articles on the process over the next few weeks which will appear on http://blog.helftone.com :-).