I don’t recommend going over to FantasticContraption.com unless you have a couple hours you’d care to dispose of.
It’s a puzzle game of sorts, where you can build simple machines consisting of wheels and sticks, then set the machine in motion to accomplish a task. Once the machine starts going, there’s no touching it until it either completes the given task, or you restart.
The game is ‘physics based’, meaning objects behave as you’d expect them to. Balls roll, blocks tumble, and a small vehicle rolling off the edge of a cliff… plummets.
The site also allows you to upload completed machines for each task, and going through other peoples’ solutions to the problem. Some are absolutely fascinating and intricate, involving dozens upon dozens of components.
Thanks (or raspberries, not sure which yet) to blk for pointing this one out to me.