Here is a little patch inspired by a PD example: you can get a square waveform subtracting two sawtooth waveforms with identical frequency (the second one delayed by half cycle). If you give one of the sawtooths a slightly different frequency you will get a pulse width modulation (the resulting square waveform width changes continuously). By changing the ratio between the two frequencies, you get more interesting results.
Here is a video demo:
Note that you get complex evolving waveforms that are band limited, since the original oscillators are band limited (and this is a good thing!).