Cramster, a global math and science study community that launched in 2003, is a place where students can interact online with teachers and their peers to help solve problems based on subjects such as physics, calculus, and chemistry. The mostly-free online community features a number of study materials, such as textbook solutions and practice exams, as well as an interactive question-and-answer board that is monitored by Cramster "Subject Matter Experts." Students can post questions, and registered teachers post guidance in response. Earlier this year, Cramster launched a Facebook application called Courses 2.0, where Facebook members can find and communicate with one another on the Cramster web site outside of the classroom. Cramster is based in Pasadena, Calif.

http://www.cramster.com