I’ve not done an in-depth look at this network but reading through their documentation shows it has a lot of similarity to the basics of the Nostr protocol and network. There is just not as much information available on the Polycentric site as there is already for Nostr. Nostr is also censorship resistant, with distributed relays doing the relaying of posts (Polycentric calls them servers). Both use public-private key cryptography, with every post being cryptographically signed. Both networks also have the ownership of the identity managed by the end client (no-one can delete a client on either network), and those profiles can be used across devices.
And whilst basic posting looks very similar (microblogging type format, and is limited to 280 characters) this is also where the differences lie. Nostr has likes, whilst Polycentric only shows boosts (reshares) and reactions through commenting.
The Nostr protocol is also an extensible one, which means it has new NEP standards added by various people to go way beyond just blog posts. So, it also already provides full length text posts (like Minds uses), events, link aggregation, and more.
Polycentric servers have a moderation API control built-in (non-recommendation vs non-storage) whilst Nostr does not have this, and it is left to individuals to block or mute a profile. But the recommendation feed is a nice touch on Polycentric to help new users find recommended content. Both networks allow anyone to host these servers/relays.
But if privacy and censorship resistant networks are what you’re into, then both Polycentric and Nostr are worth having a look at.