I'm not sure how Nostr actually works. I do get conceptually what it's about, sorta, but nowhere near a complete picture.
From what I figure it seem in many ways a superior alternative to the Fediverse. Not quite as adopted/used yet, but there's the undoubtedly better handling of portable identites.
I'm beholden to the instance operator on fediverse, but here I, as I understand it, truly own my identities through the private key I have generated. That's very nice to know.