For that, check out MediaGoblin (also implementing ActivityPub for interoperability): https://mediagoblin.org/

Now where is the reddit alternative?

It's called Usenet.

Look Usenet is nice and all but it's not a forum system and it's definitely not a reddit substitute.

It is decentralized though, which is great.

> Look Usenet is nice and all but it's not a forum system

That's exactly what Usenet is, and Usenet with 1990-era terminal clients was superior in most respects to most current web-based forum systems.

Heck, 1996-era GUI clients are also superior in most respects.

Jon Udell wrote an excellent book in 1999 on building collaborative systems with NNTP servers, web technologies, etc.:

https://archive.org/details/practicalinterne00udel

It was open-sourced, so reddit's alternative would be reddit... IIRC, the main competitor (voat) is based off of that source.

Sure while "Voat" is an alternative they're both centralized.

I'm meaning decentralized reddit.

Servers as subreddits, federated multi-reddits, only registered server accounts can vote on certain pieces, server by server moderation etc.

I had written a mostly functional system based around exchanging gpg-signed anonymous messages, usenet style a few years ago, with distributed voting, opt-in moderation, and server federation.

https://github.com/e1ven/tavern

I eventually moved on because I couldn't figure out how to solve some of the social problems, but I still think something like that could work out.

Do you have a document (or a set of issues) describing the social problems you were trying to solve? They may have already been solved, in some other context.