https://github.com/LemmyNet/lemmy is federated Reddit. It's also open source just lacks community. Some things are also already better like more performant front end. If I was to bet on something to overtake Reddit, it would probably be it.
What ultimately killed Digg was the disastrous "Digg v4" redesign in 2010. Reddit's features helped it capture the fleeing users, but it was ultimately Digg's actions that triggered the mass migration, and Digg never really recovered.
It is a decentralized link aggregator based on ActivityPub.
There are also a number of other projects using the same paradigm in various states of development. In my opinion, when these will come together and intercommunicate with one another then we can say they represent the competition.
As you can probably guess, it is a truly hateful place.
Practically speaking it is essentially (from my observation) a safe space for racism, homophobia, anti-Semitism, covid denial, dangerous conspiracy theories, misinformation, etc.
I hesitate to bring attention to the site at all because I don’t want the hate to proliferate, but I suppose it is better to know this exists rather than letting it incubate hate under the radar.
Edit: I also want to say I think anti-censorship is noble and Ruqqus, as a technology, is pretty well done. I think building a non-hateful community on Ruqqus would elevate it to be better than Reddit.
"anti-censorship" is just a euphemism for a place where someone can say the N-word without being banned.
One difficulty these days is that I am unsure how to suggest to add new newsgroups, and it seems also some other people are unsure too. (I think someone wanted to add a newsgroup for the COVID-19 pandemic, but seemed to be unsure how (I think they wanted to add it to the alt.* hierarchy); I checked just now and the Usenet provider I use does not seem to have such a newsgroup at this time. I would think that you would need to contact the hierarchy administrators, probably. Unfortunately, I do not know how.) Of course, this is not a problem with existing newsgroups.
In the case of spam, there still is some, but it seems these days the spam on Usenet are all from Google Groups. (There are legitimate messages from Google Groups too, although many of the legitimate messages come from other providers.)
NNTP does have many advantages. It is better in many ways than web interfaces are, and I think also better than mailing lists are too, although you can have all three if wanted. I know I am not the only one who wants this, to have NNTP for these things (I have seen others both on HN and elsewhere; even on Usenet they suggested even isolated forums should have a NNTP backend, and I agree).
It uses the old reddit open source code, and the administration is even based around the pyramid of debate, similar to hackernews.