2010-03-25: Recommended reading: a review and comparison of ActiveMath with other Interactive Learning Environments for Mathematics.
Jana Trgalova, Denis Bouhineau and Jean-François Nicaud have reviewed and compared state of the art Interactive Learning Environments for Arithmetic and Algebra, including ActiveMath. The results have been published in the International Journal of Computers for Mathematical Learning:
Trgalova, J., Bouhineau, D., Nicaud, J.-F. (2009). An Analysis of Interactive Learning Environments for Arithmetic and Algebra.
International Journal of Computers for Mathematical Learning, 14(3), 299-331. DOI: 10.1007/s10758-009-9155-9
The review gives a good overview and fair comparison of the different systems. Important to note: Newer ActiveMath releases provide even more (and improved) features than the ones described in the article. For instance, as opposed to the other systems, ActiveMath does not have always the same prescribed tutorial strategy for all exercises, but many custom strategies are possible. These strategies can provide coloring student's answers, give hints and solutions in solicited and unsolicited (and mixed) way.