Maybe one that doesn't even exist yet.

I'm building something that could help in this regard: https://github.com/mariusor/go-littr

It's a distillation of the early reddit into a discussion platform that speaks activitypub. This means that the goal is not to have "one site" to rule them all, but that communities can each create their own and then interact with others if they chose to.

An demo instance is at https://littr.me