There is also r/TheMotte, which formed from a schism in r/slatestarcodex. It mostly discusses culture war issues. The reason they split is that Scott was getting concerned that culture war discussion in his subreddit would attract the Eye of Sauron, which is why he asked people to make a new subreddit to discuss culture war (and also made it such that culture war discussion was now prohibited in r/slatestarcodex). Recently, however, the Reddit admins have been making moves to potentially ban the subreddit, so they are thinking about moving elsewhere.
Most of their content is centered on the Culture War Roundup thread, which refreshes weekly. Several posts are made per day.
Not personally a fan of the subreddit, as it doesn't honestly seem all that rational at the end of the day. That being said, enough people there identify with the community that it should probably be included.
For ye sweet springborn children too young to recall — know that LW is but one small isle of a grand and august archipelago!
Immediately after our community was born, we schismed a whole bunch. And now there are rat colonies (evolved and culturally drifted and not necessarily even rats now??) in all sorts of nooks and crannies, made for people who prefer them alongside or over our birthplace!
Here you can see Scott Alexander's map from an age lost to time (2014). While outdated to the precipice of uselessness, it is a beautiful expression of our community's tendency to sprawl everywhere. And it may give you a sense of the scale here!
What I hope to do is maintain an updated catalog of all these vaguely-rationalisty communities.
This is a spreadsheet including all the ones I know. I ask that others help to complete it by linking to active and public groups that share unique memeplexes with Less Wrong. If you're not sure whether a group meets these criteria but suspect it might, please include it and your peers can decide whether it belongs on this list.
I expect the sheet to eventually only take suggestions, but it is free to edit at the moment! Please feel free to edit in any prosocial way; 'tis only a draft.
I hope to find some new isles and to share some with you that you may not have known!
(h/t Jacob Falkovich for inspiration stemming from his post on ingroup)