Note that while Mastodon is the most widespread implementation, and kind of sets the de-facto standard like IE did with HTML in the 90s, there are a many other

Note that while Mastodon is the most widespread implementation, and kind of sets the de-facto standard like IE did with HTML in the 90s, there are a many other fully compatible implementations to run a Fediverse server and federate over ActivityPub. You can join or self-host any implemention and follow and communicate with users on other servers. There are moderation tools and admins can set policies for federation; some servers are picky with how they federate, some more free-speech-oriented. Fully unmoderated servers with open registration that try to federate promiscuously tend to get siloed of from the rest fairly quickly. The network is not full-mesh by design, so typically either one of two servers (or user on it) needs to either manually follow users from that server or have content forwarded from already followed actors to ingest it. The neat thing with this is how you can natively and seamlessly follow vloggers on Peertube on your personal Friendica instance, and boost it to your followers on Mastodon. People interested in FLOSS and Linux may be interested in checking out the fosstodon.org instance. I'm on a small not very active Pleroma instance hosted by friends (bio). Some people have accounts on many servers. https://fediverse.party/ https://fediverse.party/