WeBWorK is a system that allows professors to put homework problems on the web and allows students to solve these problems over the web.

Using WeBWorK, students may try to answer homework problems more than once. After each try, a message appears telling the student whether the answer is correct or not. This allows students to try to find out what they did wrong and hopefully to understand the topic of the question better.

Each WeBWorK problem set is individualized (each student has a different version of each problem, for example the numerical values in the formulas may be slightly different).

See the material at this site for much more information about WeBWorK.