Harmonographs

A harmonograph is a drawing device that is constructed of coupled pendula. Here are some instructions for how to make one based on triple pendula. Oxford's Museum of the History of Science apparently houses this one, although it wasn't there the last time I visited. I also remember seeing something along these lines (or maybe it is even an example of one?) at KITP.

And, of course, this automatically makes me think of the Spirograph drawing set that I had as a kid.

(Tip of the cap to the National Museum of Mathematics.)