The only one I found interesting was Lemmy. It looks like old reddit and it is built on the ActivityPub protocol. I've also looked into ActivityPub the last days and it seems very logical. Someone described it as email for json. The benefit is that any service on the Fediverse can talk to each other and users don't have to sign up for every service, they can just use their one identity if they want.

There are multiple instances of Lemmy. https://programming.dev/ seems like a good place to start for people on hackernews. Once you have signed up you can read and interact with other Lemmy instances as well.

The main problem they need to solve it to make it more user friendly and simple. I think a barrier for many users is to understand what ActivityPub and Fediverse is. They should put all that info in an about page, and present the login as any other web 2.0 app.

lemmy is looking like it has potential. they certainly have some critical issues to solve before it's familiar enough for plebs.

https://lobste.rs/ and https://raddle.me/ are "Reddit style" sites. Slightly different approaches to moderation and signup.

Lemmy and Kbin are the future I'd like. As siblings have said they're federated - you have an account on one, but you can subscribe to and interact with communities (subreddits) on any. This is the same way that Mastodon works - it's actually the same underlying protocol (ActivityPub).