Mastodon is individually run servers linked together using open protocols. No corporate dickheads are in charge. It is part of the Fediverse, which is way more just Mastodon. There are other microblogging services, image and music sharing, Reddit replacements, and much more.
You control your feed, rather than having it manipulated. Yes, it’s geeky. Expect to spend a little time learning it. That’s also why it’s powerful. Your feed is who you follow. You can also search by hashtag, subject, or just explore.
(Some Mastodon servers have preemptively blocked Threads, assuming it ever supports the Fediverse, which is how it will link to Mastodon. Don’t hold your breath. Facebook has a long and tired history of lying.)
Mastodon: “The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization!”
Axbom has lot of information about Mastodon and the Fediverse.
A federated social network is a system that is decentralised, developed and operated by distinct providers (something like email but for social networks). It consists of multiple social apps and websites, where users of each site can communicate with users of any of the other compatible sites.
An application or website participating in a federated social network is interoperable with the other sites (known as instances) and federates (fetching and especially pushing data) with them based on their users interactions. Communication among the social websites is conducted through social networking protocols, like ActivityPub.
The Fediverse = ActivityPub
It makes sense to view the Fediverse as encompassing all those tools and software that make use of the ActivityPub protocol.
Any social media site that does everything for you also limits what you can do and controls and manipulates what you see. Mastodon is the opposite of that. Jump on in!