Did you know that Mastodon apps can work with non-Mastodon accounts too?
Mastodon is one type of server on the Fediverse, but there are also lots of non-Mastodon Fediverse servers compatible with Mastodon apps through the "Mastodon API". This compatibility allows even new types of server with tiny userbases to have apps, although it can restrict the range of features the app offers.
There is more info about this topic and lots of questions answered at:
