I know you're probably sick of people suggesting games so much, but I think this engine would make a great racing game. It wouldn't take that long to do. All you'd have to add are start and finish lines, plus exploding or taking damage when you bang into a wall too hard. It looks like exploding would be easy considering what you already have worked out in this one.
I've never seen a racing game controlled with the mouse, and I think it would be really addicting that way. (not that it isn't addicting already)