What happens when a really old beat up thrift store acoustic guitar and some DIY oscillators (built years ago and summarily forgotten) are pulled out of storage and into play? This happens. This.
I forget the chips & particulars of the oscillators, but one accepts something like amplitude and frequency modulation from the other two. With no fancy routing or modular outboard stuff, just riding the cheap on/off toggles on the modulators and various knobs to engender variation.