I'd just like to interject for a moment. What you're referring to as Mastodon, is in fact, the Fediverse, or as I've recently taken to calling it, the ActivityPub-Fediverse. Mastodon is not a singular network unto itself, but rather a subnetwork of a greater "federated universe" - the Fediverse - realized by thousands of independent, live servers, each running an instance of one of an ensemble of platforms, all of which interoperate via the ActivityPub protocols.

Many Mastodon users surf a particular impression of the Fediverse every day, without realizing it. Through a peculiar turn of events, the fraction of the network which is most widely used today is called "Mastodon", and many of its users are not aware that it is basically the Fediverse, equally inhabited by users from other non-Mastodon servers.

There really is a Mastodon, and these people are using it, but it is just a part of the Fediverse they use. Mastodon is an ActivityPub server for microblogging. Mastodon is an essential part of the Fediverse, but limiting by itself. The Fediverse experience manifests in the context of a complete network. Mastodon distributes content in combination with other ActivityPub servers. The whole network is basically ActivityPub servers with Mastodon being the most common; The so-called "Mastodon network" is really the Fediverse network.