Cramster
Cramster is a study community comprised of students and teachers helping each other to solve problems in mathematically-based subjects like chemistry, physics, and computer science; mathematics courses such as calculus and statistics are also covered. Cramster creates and provides access to study materials (textbook solutions, topic notes, sample problems, and practice tests) along with materials developed by community members. The Cramster Answer Board, which is moderated by subject experts, furnishes community members with an opportunity to ask and answer questions. Basic membership is free, but registration is required. Premium membership, with additional benefits, is available for a fee.