I've already mentioned that OpenSim has entered the Fediverse several months ago, and that there are even two dedicated Mastodon instances for OpenSim users. One is opensimulator.social (
https://opensimulator.social/), run by Buzzy Cnayl of VivoSim (formerly Quintonia, see news below). The other one is opensimsocial.com (
https://opensimsocial.com/explore), run by Lone Wolf.
But the Fediverse has more to offer than "Twitter clones" like Mastodon. With Reddit messing up big time currently, the time has come for the "Reddit clones" Lemmy and /kbin to grow.
And just a few days ago, Hyacinth Jean has started a Lemmy community (= subreddit) for OpenSim:
https://sh.itjust.works/c/opensim/
If you already have an account somewhere in the Fediverse, e.g. on Mastodon, you can use it to join Lemmy communities. If not, or if you find that too inconvenient, feel free to join Lemmy instead.