Audio rate chaotic oscillator - Magpie Modular Black Custard Panel
https://www.modulargrid.net/e/nonlinearcircuits-brain-custard
https://modularaddict.com/magpie-braincustardblack-panel
http://nonlinearcircuits.blogspot.com/2016/01/brain-custard.html
Available as an assembled Module and as a DIY project.
This Module is currently available.