GoGrinder

This program would be perfect if it incorporated some sort of spaced
repetition in which new problems are treated like flash cards using a
technique like supermemo, fullrecall, vtrain, or memory lifter. The idea
is that when you are learning something new, you'll forget it at a certain
rate, and taking advantage of that rate you can avoid repeating material
that you know well and focus on material you need to review or learn.