reddit.com has a subreddit for just about every single subcategory you can think of
Yes, and the vast majority have nothing to do with tech, and some of them, even the more obscure ones, have large, involved communities.
What are some?
What are you interested in? The ones I participate in areas very niche. It's hard to say because it's like recommending a specific Web sites on the Internet. Just pick a topic and search.