This VCO is based on a sine wave. The sine wave is shaped in its positive and negative swing by two mapper nodes that are fed through arctan (tube distortion) expressions. You can fade between pure sine and shaped signals.

It's a deceptively simple module with a lot of different tone combinations. To prevent aliasing, make sure the far left and right mapper breakpoints are kept to the extreme positions and just move the central breakpoints. Putting any distance between the outer breakpoints will cause sharp jumps in the waveform and introduce harmonic distortion (which you may also enjoy!).