Nostr and Mastodon both respond to platform centralization, but they take different architectural routes. Mastodon uses federated servers with accounts hosted by instances. Nostr uses user keys, clients and relays.
Identity model
In Mastodon, an account usually belongs to an instance. In Nostr, the identity is a public key that can be used across clients and relays. That difference changes portability, moderation, UX and recovery.
Server model
Mastodon servers are communities and account hosts. Nostr relays are event transport and storage points. A Nostr user can publish to many relays and read from different relay sets.
Moderation model
Mastodon moderation is instance-centric. Nostr moderation is split across relays, clients, lists and user choice. Neither model is automatically better for every use case.
Crays view
Crays needs portable identity across digital profiles and real venues. That makes Nostr more aligned with the requirement than an instance-hosted social account, although lessons from federated communities remain useful.