Ask HN: HN-like sites for other disciplines?

Hacker News isn't like any other tech news aggregators or forums. The comment sections are filled with a high standard of often very specific domain knowledge, and it's a common occurrence to see 'high profile' (to us) names. You might ask about an esoteric piece of software from decades past and have a response from its creator, or someone who knew them, who worked alongside them.

What are similar niche high-quality online spaces for other fields?