http://areeweb.polito.it/didattica/polymath/
http://mathsite.math.berkeley.edu/main.html
http://matematica.unibocconi.it/
http://www.maths.gla.ac.uk/~wws/geomlink.html
http://www.storyofmathematics.com/index.html
http://www.cut-the-knot.org/content.shtml