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.
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.
It uses the old reddit open source code, and the administration is even based around the pyramid of debate, similar to hackernews.