MathOveflow is a young (started in 2009) and active online community of research mathematicians and graduate students, where users to ask and answer research level math questions, the sorts of questions you come across when you're writing or reading articles or graduate level books. (E.g., "Is there an X that does Y" or "Can this hypothesis in that theorem be relaxed in this way?")
I will talk about the idea, what it took to start the community and why it works particular well for the pure mathematics research community, and share some amazing stories of research collaboration happening through the site.
