There are certainly other social news sites, but Lemmy and Reddit are by far the most alike. Most critically, they both are focused around segmenting into user-created and user-moderated sub-communities. That’s as opposed to sites like Hacker News that are also social news sites, but only have a single feed or Slashdot where the topics are chosen by site admins.
Digging via https://alternativeto.net/software/reddit/?license=opensource&p=1 Here’s some of the 55 results :
I think Aether is cool. It’s a P2P app that, with enough active users on a board, allows for mod elections. Only problem is that a fair amount of the active userbase is alt-right adjacent or straight up Fascist. I have seen some Leftists posting on there, but I think it’ll take more Leftist users to change the culture.
Postmill looks really good but I don’t see any mention of federation on its homepage.
Checking their Gitlab description it looks like you are right. The OP mentioned Reddit in the post title though, and Reddit is “still” not federated ;-) Using https://fediverse.party I found these as well :
saidit dreadit theyre both kinda dumpy