Quadrature Oscillator
Low frequency to audio rate quadrature oscillator, outputting 4 sinewaves 90 degrees apart.
Based around two self-oscillating filter, it features a buffered frequency modulation input with attenuverter, a switch to cover 3 frequency ranges and fine tuning.
https://syntonie.fr/produit/vu006-quadrature-oscillator/
Available as an assembled Module and as a DIY project.
This Module is currently available.