A kittable version of the Lockhart wavefolder popularised by Ken Stone in his CGS52 module, albeit with a difference or two.
With this module, it's possible to control the amount of current running through the positive and negative arms of the wavefolding section, which can lead to some interesting results irrespective of whether you're fettling VCO or control voltages.
The 'main' output gives the folded waveform whilst the 'square' output will, under certain circumstances, give an arrhythmic pulse train which can be used either as a modulation source or a square-wave oscillator in its own right. Keep in mind, though, that the depending on the biasing of the transistors you may not get anything out of the square output despite there being a folded waveform present on the 'other' output.
Works best with sine or triangle-based waveforms but there's nothing to stop you putting, well, anything into it - altering the level of the input signal can lead to some very interesting filter-like effects. If you really want to fatten up a sound, run it through a low-pass filter (or any filter) before feeding it into the wavefolder. Works really well on basslines if you use a resonant filter.
Finally, on a technical note, the input signal must be at least 1.4V p-p - this is due to the voltage drops created by the two transistors in the circuit; the practical upshot is that this module will not work with audio signals unless they're amplified (a lot!) whereas most VCOs and CV generators will work just fine.
The BOM and schematic can be found at: https://bitbucket.org/yorkmodular/4hp-wf-kit/src/master/
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