There’s the Bridgy Fed project which has ActivityPub and Bluesky support with Nostr planned. This is designed very much as a ‘bridge my content / feed’ model.
On the other end of things, there’s the Mostr which bridges ActvityPub and Nostr and a newer Ditto/soapbox bridge that nostr:npub108pv4cg5ag52nq082kd5leu9ffrn2gdg6g4xdwatn73y36uzplmq9uyev6 is working on. Mostr is live now, I use it every day. Unfortunately it’s been defederated by a number of fediverse servers. I think a single automated gateway for all of nostr is unlikely to work well with the fediverse.
In nos.social you can enter mastodon style @rabble@mastodon.social style fediverse user names and it’ll pull their feed through mostr. That works well today, I use it all the time.
