Comment by kratom_sandwich

http://www.datatau.com/ gets mentioned occasionally for data science, but there doesn’t seem to be a lot going on in terms of comments

https://www.bogleheads.org/ for finance and investing

https://lobste.rs/ for tech, slower than HN

Also, here’s a starting point for your search from a previous thread: https://news.ycombinator.com/item?id=29214788