Here is a fun little audio toy to play with. Nowhere near as cool as Michael Mahon’s toys, but it has some neat features: High Frequency Oscillator sampling a Low Frequency Oscillator’s waveform with envelope control. You will hear that the upper octave gets out of tune: a feature of having a minimal 100 cycle sampling loop. Just ignore that octave if it annoys you. Try playing with the LFO at a value around 4-8.
This was also an experiment in embedded PLASMA, thus its location along with the source.
The link to a bootable floppy image that lets you jump right into it: https://github.com/dschmenk/PLASMA/raw/master/src/samplesrc/a2pwm/lfo.po