An oscillator:
I built this for my workbench, hence the pin sockets for power and outputs, but it could be adapted for synth use. Circuit is the variable waveshape LFO by Kassutronics. I left out the sine shaper for simplicity and I socketed the integrator cap (C5) so I can switch frequency ranges easily — right now it’s 2.2 nF for audio frequency. “Shape” pot varies the width of the pulse output and varies the TRI/RAMP output from sawtooth to triangle to ramp.