First and last PD external of 2017: a band-limited impulse train which can be used to generate nicely sounding band-limited oscillators and modulations.
Based on [Stilson and Smith 1996]: https://ccrma.stanford.edu/~stilti/papers/blit.pdf.
Inlets are signal-only. Respectively: pulse frequency (Hz), number of harmonics (limited to the maximum allowed at that frequency), bipolar/unipolar output (< 0/>= 0).
The harmonic content variation is phase-locked to avoid discontinuities, so there is a delay <= to the pulse period before those variations take place. (Very tiny in most cases.)
Happy new year!