zlacker

Metafilter certainly comes to mind. Though I believe it's well below HN in scale.

On Reddit, there are several immensely moderated subs with persistent high quality, and millions of subscribers, notably /r/AskScience and /r/AskHistorians (though also numerous others).

Smaller subreddits are relatively easy to maintain at quality, though sustaining engagement is hard (much of the Reddit dynamic actively works against this). Keeping large subs sane is exceptionally difficult. Getting "defaulted" (being added to the list of default-subscribed subreddits) was long seen as the kiss of death for smaller, quality, subreddits.

>>dredmo+(OP)
I've seen some extremely toxic political discussion on metafilter.

>>astrof+9d1
Are they commonplace, moreso than most / many other sites, and is MF otherwise restricted to cat pics?

Or are many discussions on MF generally constructive and productive?

My experience, dipping into it (I'm not a member/regular) is the latter. Backed by some quantitative/qualitative research:

https://old.reddit.com/r/dredmorbius/comments/3hp41w/trackin...