PHS simulates a 4-pendulum harmonograph.

To show you the kinds of patterns this
program can generate, use the mouse to
move the pointer to the blue area labeled
"Auto-Randomize", then click any button.
When you see a pattern you like, click anywhere
on the screen to stop Auto-Randomize.

A real harmonograph has pendulums connected
to a pen and paper that move the two back
and forth to create circular patterns.