(Repost from last time Mastodon was on the front page)
There are a multitude of Mastodon-compatible ActivityPub implementations[0][1]. Save for bugs, which devs and maintainers tend to be motivated to work out, they should all federate together, meaning you can follow and share between them. All have instances with open registrations and are also straightforward to self-host. 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.
For those of you raising issues with ways in which the AP-speaking fediverse is lacking at this point, many of these points are acknowledged by members and implementers of the community. The biggest one IMO being the same challenge other federated and P2P communication systems (like Matrix) need to solve: DIDs, which should make users less under authority to their server admins, and server owners less under the authority of ICANN and registrars. The second one (which follows DIDs) being more effective models and tools for moderation and curation.
If you're actually interested in exploring constructive conversation on how to move forward to where we don't need to rely on centralized authoritarian incumbents and getting a healthier ecosystem, come join in[2][3][4].
[0]: https://fediverse.party/
[1]: https://fediverse.party/en/miscellaneous/
[2]: https://codeberg.org/fediverse
[3]: #socialcoding-foundations:matrix.org
[4]: https://pad.public.cat/8yNgnlxmSsGYk3TfIau46A?view