https://sonic-pi.net/ is neat; its in Ruby and very mature project but it requires you to run their own custom IRB application. But beyond that its really easy to use, and probably the most sophisticated that I have seen. Accidentally went to one of their talks in Berlin years ago.

Ooh thanks, this looks really interesting.

Not exactly programmatic, but I saw another streamer hook up their chat to super collider so folks could do a collaborative jam session. It was chaos, but a lot of fun.

(and for anyone not familiar with supercollider: https://supercollider.github.io/ - it’s open source software that’s “A platform for audio synthesis and algorithmic composition, used by musicians, artists and researchers working with sound.”)