I work for an org that makes a bunch of privacy protocols. Semaphore, RLN, and MACI. All of these use zero knowledge cryptography. Semaphore is a way of proving you are part of a group but without revealing who you are, RLN is the same thing plus spam resistance, and MACI is “minimal anti-collusion infrastructure” which is voting while trying to prevent bribery.

I imagine this is a bit outside of what you are asking for but thought I would share