The State_of_the_Art_in_mathematical_e-learning paper seems to have overlooked WeBWorK (http://webwork.math.rochester.edu) (full disclosure: I'm one of originators of WeBWorK.) You might like to have a look at it. There are various schemes to integrate it with moodle, (e.g. moodle bridge ) some of them are waiting on the RQP module settling down, but it will happen eventually.
Anecdotal data shows convincingly that homework with immediate feedback has the effect of having students spend more time at their homework and having them asked more focused questions. Statistically backed conclusions are being written up and should be published soon.