This is a great app for students who are practicing for math aptitude SAT tests, or just to test your math aptitude! Xenakis MathGame tests math skills by presenting graded math problems.
The latest version has detailed hints and explanations. Explanations are written to provide the most useful information to students preparing for math exams.
There are hundreds of problem types and subtypes, with grades from Kindergarten to Grade 12, and with each problem parameterized with random values, so that there are effectively tens of thousands of different problems. This is a great tool for students, because you can play it literally for days and constantly see new problems displayed.