Available as an assembled Module and as a DIY project.
This Module is currently available.
Quadrature generator
Unlike the phase shifters we all know and love from guitar pedals, which superimpose a phase shifted signal on an unshifted signal to generate notch filtering, this module generates a pair of outputs whose harmonic content is unaffected, but whose harmonics are all shifted 90 degrees away from each other. This is useful for driving something like our Boethian Wheel, or indeed the inputs to a vector scanner such as a Vectrex or display laser.
Based on the classic all-discrete design, this is a very straightforward DIY build, with only a sine wave oscillator and dual-trace oscilloscope needed for final setup.
These merchants probably sell this module. Huh?