Threw together a comparison of the four decentralized social protocols I know best: IndieWeb, ActivityPub, ATProto, Nostr. Obviously oversimplified, hopefully still useful! Preview below, click through for full table with links.
I tried to focus on how these protocols are currently deployed and used in the real world. For example, identity in ActivityPub is technically URL-based, but in practice the fediverse uses WebFinger
user@domain identifiers more or less universally, so the table reflects that.
Feedback is welcome!