This looks like a lot of pointless fun!
How about a rolling-ball binary digital mechanical computer?
Sadly out-of-production, but seems pretty doable using multiple layers of plywood…
I love that!
Maybe if enough of us bug them they would open source the plans.
Mathias Wandel has so many great inspirations on his site. Here’s his marble contraption page. I have learned so much about woodworking technique from him.