I'm working on a game -- when time allows -- that lets you build and race vehicles using Lego Technic-style pieces, e.g. gears, motors, belts, blocks, etc. It's honestly pretty easy from a tech perspective (I'm using Python + PyOgre + Bullet for the core of it), but presenting the vehicle designer to the user in a nice way is really tough. I'll announce the alpha here as soon as I have anything, of course.