Math Overflow

article about MO: https://simonsfoundation.org/mathematics-physical-sciences/news/-/asset_publisher/bo1E/content/the-global-math-commons

MathOverflow turns one year old today: http://meta.mathoverflow.net/discussion/684/happy-birthday-mo

I like to think MO is the game layer on top of math. See http://www.ted.com/talks/seth_priebatsch_the_game_layer_on_top_of_the_world.html

Article about MO in San Jose Mercury: http://www.mercurynews.com/science/ci_15713739

check out MathOnline, a site that aggregates and organizes freely available online math resources: http://mathonline.andreaferretti.it/