- Encyclopedia of Mathematics
The Encyclopedia of Mathematics is a wiki and as such an open access resource. The wiki contains the original articles from the online Encyclopaedia of Mathematics, published by Kluwer Academic Publishers in 2002 which then consisted of some 8,000 entries, illuminating nearly 50,000 notions in mathematics. The site is continuously updated.

- WolframMathworld
WolframMathtworld is an online encyclopedia containing some 13.000 entries as well as a number of interactive features. Covers subjects such as algebra, applied mathematics, calculus and analysis, discrete mathematics, foundations of mathematics, geometry, history and terminology, number theory, probability and statistics, recreational mathematics, and topology. Edited by Eric W. Weisstein with assistance from thousands of contributors around the world, the site is updated daily.