Really fun topic. A few years ago I spent a month churning out procedural music each day, and I'm still kind of happy with some of them.

E.g. this pseudo-fugue: https://fenomas.com/2017/12/advent-18/

Or this chiptune jazz standard: https://fenomas.com/2017/12/advent-17/

(caveat: sounds are all dynamically generated from WebAudio oscillators/filters/etc, so the audio might skip on mobile CPUs.)