@smitty :) not only mastodon. Mastonon is one of microblogging engines of Fediverse (others are Misskey, Pleroma, e.t.c.).
But Fediverse is not only microblogging. There are pictureblogging platform (Pixelfed, like Instagram), videoblogging (Peertube, like Youtube), macroblogging (Hubzilla, Streams, Friendica, e.t.c.) and other.