The Oscilloscope Artist originally appeared in the November, 1975 issue of Popular Electronics. It creates all sorts of fascinating moving geometric patterns on an oscilloscope screen.
All you need is a low bandwidth 'scope with horizontal and vertical (XY) inputs.
A reconstruction of the complete article is in a pdf file. All the original parts are still available!
The original block diagram is a bit confusing so I redrew it. Oscillators A & D create a Lissajous figure baseline from triangle/square waves. Oscillators B & C are multiplied and summed with A & B.
I've also used it with a laser projection system with X and Y galvos and it works although the corners aren't too sharp.