Support Polycentric protocol

[snarfed]

New protocol to me. Users are keypair-based, protocol is relay oriented, like Nostr. Protocol docs say messages are synched via set reconciliation, eventual consistency, but I can't tell if that's client <=> relay or between relays themselves.

https://harbor.social/ is maybe the main app. It also does an identity linking/verification thing? https://docs.polycentric.io/harbor/ :

Harbor is an identity management system built on top of Polycentric. Harbor can be used to link identities across the web, make arbitrary claims, and manage endorsements of other users. It is conceptually similar to the PGP Web of Trust described by Phil Zimmerman in 1992:

https://polycentric.io/ and https://futo.org/ are other clients, https://chat.futo.org/ looks like developer chat.

No blockchain. Haven't found any usage numbers yet.