Zero knowledge proofs but with the 21million cap. Kinda like an in-between of monero and Bitcoin. It's not private by default.

I decided to buy about a hundred dollars almost exactly a year ago just to test it out and see if it was useful, I wasn't that impressed tbf but at least it got a fun little return for me that I can throw back in btc/xmr.

In general though I would typically reccomend for most usecoses that might call for something like zec just using btc privacy tools if possible instead coinjoin/silent payments etc. and if that level of anonymity isn't sufficient then I would just recommend using xmr at that point. But maybe there is some weird/specific use case I'm not yet aware of.