Another proof of the Pythagorean Theorem. This one is by Leonardo da Vinci (citation from Proofs Without Words II by Roger B. Nelsen.

Print two copies of the tray, one each of the squares, and two triangles.

This is still a work in progress. Suggestions about how to make the tray easier to use are very welcome! There is a hole in the tray that you can put a bit of 1.75mm filament in to attach the two pieces together and let it "spin." This works, but the join is very weak.