Spirograph online
A gear rolls inside a ring and a pen in the gear traces the curve. Change the gear size and the pen position for different patterns, and press Draw again to layer another color on top.
The page tells you how many times the pen goes round before the pattern repeats: it is the gear size divided by the largest number that divides both the gear and the ring. For spirographs to color in, see the mandala coloring pages.
Pen