mine is perhaps a mastodon with dislikes
a loops like but for youtube shorts instead of tiktok
email (i am not technical but since it is hard to self host email what if someone made a email that could be self hosted that is a part of the fediverse)
and a facebook like that isnt outdated as friendica
Letterboxd, and to an extent Goodreads.
I just spent a solid chunk of time importing and correcting various accounts to NeoDB and Bookwyrm and they are both petty frustrating to use, especially with how much content is missing, mislabeled, or duplicated. Plus, they don’t seem to federate with each other (understandable, in so far as very few parts of the Fediverse actually federate well together [unlike, perhaps, Mastodon and mbin]) or even support exporting/importing data from each other.