StackOverflow - Always been taking from the community (mostly googling), now trying to be part of it and contribute if, by chance, I know something that can help.
Bicycles - All mountain biker on a Canyon Nerve AM.
User Experience - When I've found this site, I had to sign up.
Q&A for professional and enthusiast programmers
Q&A for user experience researchers and experts
Q&A for professional programmers interested in conceptual questions about software development
Q&A for people who build and repair bicycles, people who train cycling, or commute on bicycles
Q&A for people studying math at any level and professionals in related fields
Q&A for peer programmer code reviews
Q&A for computer enthusiasts and power users
Q&A for professional and independent game developers