Another upvote for modular synth. Andrew (https://www.nonlinearcircuits.com/) has some amazingly cool devices.

Chaotic orbits for "waves", running audio through cmos gates to produce pitch changes, running ADSRs through a filter to produce more random envelopes,... and he seems to come up with new module ideas monthly if not more often.

My most favorite recent module of his is based on cellular automata.

https://www.nonlinearcircuits.com/modules/cellular-automata