As others have said, there are great ones about various niches. People tend to really know each other over time (in a more personal way than your Reddits of the world) and thus find themselves more accountable to each other--but it is still as anonymous as you want.
You get too big of groups or absent or poor mods and things tend to fall apart. Tens of thousands of users is no problem because most users are mostly lurkers anyways.
Quick plug--low odds here, but if you by some chance happen to know the board game Heroscape, have a look at www.heroscapers.com/community for a well functioning, respectful, fun (not modern looking) niche online community. The game has been cancelled for years, but there's still a good chunk of us active. Lots of site activity takes place in various private sections of the site devoted to various projects so you don't see everything happening but the public stuff is representative of how people treat each other there in private.
You get too big of groups or absent or poor mods and things tend to fall apart. Tens of thousands of users is no problem because most users are mostly lurkers anyways.
Quick plug--low odds here, but if you by some chance happen to know the board game Heroscape, have a look at www.heroscapers.com/community for a well functioning, respectful, fun (not modern looking) niche online community. The game has been cancelled for years, but there's still a good chunk of us active. Lots of site activity takes place in various private sections of the site devoted to various projects so you don't see everything happening but the public stuff is representative of how people treat each other there in private.