[IanHalbwachs]

I'm intrigued. Anywhere I can hear some examples of this, or know of any (free) ways I can generate some with software?

[gylterud]

Instruo Neoni is one oscillator which can do it. I think one can get on VCV rack (which I think is free).

The Neoni is demonstrated here: https://youtu.be/kkAagua3NN4 (Symmetric TZFM starts around the 57 minute mark).

Here is a track I made using TZFM (I am no muscician, just experimenting): https://hakon.gylterud.net/snd/foot-stomp.flac

The only sound sources are a TZFM oscillator and a kick drum.