Nostr is a protocol, not a platform. So, there's no rules or server admins deciding what can and can't be used on the network.

There's a heap of things on nostr that can't be bridged to the fediverse. Only basic notes get bridged. That's the only nostr stuff that's compatible with the fediverse.

Long form notes, streaming, communities (reddit clone with moderated subreddits), the marketplace, chat (discord clone), encrypted messages and Bitcoin, lots of Bitcoin getting zapped around on nostr.