how "Mastodon fits into the much larger concept of the Fediverse... visualisation ... many different use-cases and benefits of different services".
Good intro to the Fediverse as a whole, plus the visualisation in png & pdf, and some Q&As covering multiple accounts ("a user preference"), Nextcloud (adding ActivityPub end 2022). Wordpress & Drupal (ActivityPub plugins available) & Matrix, which "fits all the characteristics of a Fediverse protocol".
Note that by this definition the Fediverse is larger than ActivityPub: "protocols will come and go... [other software] are not questioned as fediverse-included: such as Zot... Matrix is most definitely Fediverse software... [also] by some measurements it is the second-largest protocol... One ActivityPub application already working on Matrix protocol support is Socialhome... today supports both ActivityPub and diaspora."
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