Phase Locked Loop Fuzz Pedal

Pilule is both a fuzz with a peculiar decay and a PLL circuit that
can shift your note several octaves up.
In its most extreme settings, the PLL acts like a waveshaper, changing
character depending on the pitch of the incoming note. Alongside
octave-ups, you may also hear octave-downs, fifth-downs, and
vowel-like filter tones.
Pilule can behave polite and smooth, but it can also get wild and
glitchy — it often surprises.

https://glou-glou.org/pilule/