Other use cases for the fediverse

I never got into mastodon because I couldn't connect multiple instances. I like this a lot about Lemmy so far (just here for a few minutes though).

Reading about the fediverse got me thinking. What other use cases could you think of? Maybe outside social media?

Would a fediverse password manager be more or less secure than some company owned pm?

How about "clones" of other social media like FB and Insta, TikTok?

What about a blogging community like Medium?

Other ideas?