"PlanetMath is a virtual community which aims to help make mathematical knowledge more accessible. PlanetMath's content is created collaboratively: the main feature is the mathematics encyclopedia with entries written and reviewed by members."
How mathematics affects our daily lives in sociological, economic, and historical perspectives. Three volume set, 490 articles, published in October 2011
Nice list of resources from around the world, some of the sites are not in English, but most are. Worth looking at as there are a lot of connections to other topics.