This site provides an extremely large collection of material related to mathematics; in fact, it claims to be the world's most extensive collection of educational and reference material on math. The site has won many web awards. It contains both encyclopedia-type reference material and animated/interactive material. It includes many opportunities for interaction and feedback to the author. Pages can be accessed by alphabetical listing, by a full-text search feature, or through a well-conceived subject categorization scheme with extensive cross links.
Please see the related reviews of the href="http://www.merlot.org/artifact/PeerReviewDetail.po?rOid=1010000000000059482">World
of Mathematics-Animations and Interactive Applets subsite, the href="http://www.merlot.org/artifact/PeerReviewDetail.po?rOid=1010000000000059486">World
of Mathematics-Probability and Statistics subsite, and the href="http://www.merlot.org/./artifact/PeerReviewDetail.po?prOid=1010000000000059490">World
of Mathematics-Recreational Mathematics subsite.