With a development team that includes several well-regarded mathematicians and other such folk, the S.O.S. Mathematics website is a high-quality resource for persons who might find themselves in need of a bit of refresher on topics ranging from algebra to differential equations. Started in 1995, the site currently includes more than 2500 web pages that contain concise explanations of topics that can sometimes be quite confounding. Visitors can use the search engine provided on the homepage, or click on one of the primary sections, which include differential equations, matrix algebra, and complex variables. Within each of these sections there are many more subheadings that provide even more information. Of course, in the unlikely event that one’s question cannot be answered by one of these pages, there is also the “Cyberboard” feature, which allows users to post their own question on one of the many message boards.