I'd just like to interject for a moment. What you're referring to as Mastodon, is in fact, Fediverse/Mastodon, or as I've recently taken to calling it, Fediverse plus Mastodon. Mastodon is not a social network unto itself, but rather another free component of a fully functioning Fediverse made useful by the GNU Social interoperability, networking tools and vital system components comprising a full Fediverse as defined by the GNU Social standard.

Many users run a modified version of the Fedivers