I think a lot of similar-ish communities happen on subreddits. I would venture to say that most other fields don't have either (1) the inclination and ability to run and moderate an independent site or (2) the sheer stubbornness to "not be Reddit" that I see on here.

Forums are also still a thing, and many have thriving close-knit and heavily-moderated communities for people of a common field or interest.