Spiro Draw

Spiro Draw is the plastic spirograph set from a childhood desk drawer, running on its own. A small toothed wheel rolls around the inside of a larger ring with a pen fixed through one of its holes, and the line that pen traces loops around the centre over and over, never quite retracing itself, until eventually it comes back to exactly where it started and the pattern is complete. Then it picks new settings and starts again. The colour of the line walks slowly around the spectrum as it draws, so a finished figure is banded rather than flat.

The two sliders are the two holes in the physical toy. Wheel sets the size of the rolling gear, which controls how many points the finished star has — and because the wheel sizes offered are all prime relative to the ring, every pattern runs the full number of turns before closing rather than shutting after two loops. Pen sets how far from the wheel's centre the pen sits: near the middle gives soft rounded rosettes, out near the rim gives sharp spiked stars with deep notches between the points.

Leaving the gear overlay on is worth it. You can see the small wheel rolling round the ring and the arm swinging out to the pen, which turns an abstract curve into something you can follow mechanically — the moment where the wheel comes back round and the line finally rejoins itself is much more satisfying when you can see it coming. Speed controls how fast the pen travels, from a slow meditative crawl to finishing a figure in a couple of seconds. Free in the browser, nothing to install.