Two of my favorite things in my life as a freelance software developer are BNI and Stack Overflow. They are both quite different things, yet some of the reasons I like them both are actually somewhat related.
BNI is the largest organization of its kind in the world. It's an organization that helps members use word-of-mouth to grow their business. It does this by being nothing but a referral-centered organization. Members meet, and do business by referral. They build relationships, and develop friendships, as a result of course. But BNI does not try to be a social organization. It focuses members' time and effort on helping each other grow their businesses.
Stack Overflow is a question and answer site. There are hundreds of these out there. Thousands. Millions, probably. You'll see most of them referred to as "Q&A Forums". Stack Overflow is not a Q&A Forum. It is not a place where people can go and randomly ask for opinions, or try to get someone to help them with a project they have no idea how to complete. It is, instead, a structured site with definite, clear rules about how to ask questions, and what is expected of you before you ask them.
So, what do I like that are similarities between these two, quite different things?