WeBWorK is supported by a grant from the National Science Foundation and has already been adopted by a number of universities.
Much additional information is available at the above site.
The student downloads a copy of the assignment, does as many problems as he or she wishes and then logs onto the internet and enters their answers into a web browser. The individualized nature of the problems means that students can work together, and yet each of them has to enter the answer to his own version of the problem. WeBWorK does not seek to replace conventional teaching, rather, it increases the effectiveness of assigning homework. Students using WeBWorK know when they are succeeding and when it is time to seek help. We consistently find that more than 80 percent of the students continue to work at their WeBWorK problems until they have all the answers correct.