I am using Moodle for 9 years now for technical trainings for personell of production companies like mechanics and operators. The average age is around 38-55 years and the "forgetting curve" increases with the age of the people. http://en.wikipedia.org/wiki/Forgetting_curve
I saw that https://www.drillster.com/ has a nice solution. It seems to be possible to integrate Drillster in Moodle.
A New Spring has the memotrainer. Have a look at:
Is there anybody out there who has a similar solution to be used in Moodle 2?