I remember having a Spirograph as a kid and being obsessed with it. Its geometric patterns are hypnotic and gorgeous. I also love generative music composition. So bringing those two things together in a browser tab, I’m hooked. Musical Spirograph is a relatively simple concept. A set of points dash around the screen according to mathematical equations, generating hypotrochoids and epitrochoids. Those points pass through a series of concentric rings which trigger specific notes.
Honestly, that alone is fun enough, but you can customize it quite a bit. There are six different virtual rotors to pick from, you can have up to three arms drawing simultaneously, and there are a bunch of other parameters to tweak the pattern. Then there are six different scale options, or you can completely customize the notes, and there are six different synth presets. Plus you can change the quantization and BPM, or even expand the number of rings out to two octaves.
Sure, the sound engine isn’t great, and it’s prone to clipping and artifacts. And I really wish there was a way to get MIDI out of it to control other instruments. But it’s still a ton of fun to get lost in for a while.