The next morning, I checked it out. It is one of THE COOLEST things I've ever played with.
It's an interactive realtime 2D physics simulator. You can call stuff out of nothingness, and as soon as it materializes, it falls, flows, and slides, according to the properties you set for it. Simple machines like gears and levers Just Work, emergently from the simulated properties of the stuff you make them out of.
It works on Windows, Mac, and Linux.
Go play with it.