Lemmy is probably the closest thing you'll find in activitypub/fediverse https://join-lemmy.org/instances https://join-lemmy.org/instances https://lemmy.world/

Lemmy is probably the closest thing you'll find in activitypub/fediverse https://join-lemmy.org/instances https://join-lemmy.org/instances https://lemmy.world/ https://lemmy.world/ the second link goes directly to the largest instance. It has all the same federated interoperability features that Mastodon or Bluesky have, but with a thread/topic format instead of a microblog format.