Mathematical Atlas Online
vitaly.friedman writes "Whether you are looking for Complex analysis, Differential Equatiions or Probability and Statistics references, the Mathematical Atlas covers the whole area of mathematics and related subjects. The so-called 'Gateway to Mathematics' is a collection of articles about aspects of mathematics at and above the university level, but (usually) not at the level of current research. "The goal of this collection is to introduce the subject areas of modern mathematics, to describe a few of the milestone results and topics, and to give pointers to some of the key resources where further information is to be found. Like any good atlas, we try to present several ways to look at each area and to show its relationship with neighboring areas and sub-areas."
From the site: "This site last updated (and all links checked) 2002/04/1"
It's a cool project, but man, it's ugly.
Overall, kudos for the content and generally improving the web.
But it does give a good overview of what a given broad topic is all about, in relatively layman terms. (Something MathWorld is not particularly concerned with.) And one thing it does offer that MathWorld doesn't is lists of resources for learning about the topics. Mathworld just has citations.