What are your favorite lesser known subreddits?

There's a lot out there that many of us might never think to search for. Most of my favorites were stumbled upon. I'll start with some of my favorites.

r/explainlikeimfive - I'm often seeing things here that I've wondered myself and could never wrap my head around. Lot's of great questions and replies here.

r/carlhprogramming - I'm bracing for an educational path in software engineering and this subreddit, combined with computerscienceforeveryone.com has made me comfortable taking my first steps and taught me a lot.

r/stopsmoking - I haven't stopped yet, but everyday I get to see tales of peoples victories over smoking on my front page. I'm slowly learning from it that it doesn't have to be so dramatic.

r/creepygaming - Because if there's two things I like, it's video games and being creeped out.