The beta for groups will release later this week, which won’t be federated initially. Federation will be added afterwards.
Looks like it will have some interesting features like videos, polls, and events, as well as moderator tools like limiting what a user can do.
Some links:
https://mastodon.social/@dansup/110931821965407984
https://mastodon.social/@pixelfed/110931868347117511
In case you haven’t seen it yet, I’ve compiled a fairly sizeable list of focused instances. More would be cool, but there’s a fair number to check out already.