There actually is a fediverse TikTok equivalent being developed! I’m not sure what the current status of it is, but it does already have rudimentary functionality. I bet the developer(s) might appreciate some help working on it, if anyone has the time/coding skills/money/etc to contribute. Somebody else mentioned Tumblr, and that exists too! So many cool projects being worked on, I regularly check this list to see what’s new, and it’s really heartwarming to see all the work people are putting into making the fediverse such a awesome place. There’s even a Tinder-esque dating app!
Personally, equivalents I would love to see include:
Archive of Our Own
RPC/F-List/roleplay platform
(I’m actually trying to work on one of these myself, but I’m an amateur so don’t get your hopes up lol)
Etsy
Ravelry
A search engine
(And not just a metasearch using the same index as Google/Bing/etc)