Virtual Harmonograph emulates a real-world harmonograph, except you can have any number of pendulums. Drawing a harmonogram on a flat 2-D surface you can have up to 4 pendulums. Two of them control the horizontal and vertical movement of the pen, and two of them control the movement of the drawing surface. With the virtual harmonograph you can see what would happen of you could have more than four if you'd like.
The virtual harmonograph also allows you to rotate the drawing surface back and forth. Think of it as a swing. You can wind it up and let go and it will unwind then wind back up again until it runs out of energy.