IMHO if there's any take away from the last 20 years of the internet, it's how hard it is to have decent communities of people online, curated like a blooming garden of diversity. What are some online communities that you appreciate?

I have a Ph.D. in neuroscience with exactly 20 years of experience. I talk about what I know and try to be curious about what I don't know. HN really helps me on both counts. How does it help you?