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 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).