It would be amazing if Khan Academy had a fact fluency practice area for the four operations that I could monitor as a teacher.  Ideally, it would incorporate both strategies and timed practice.  There are a number of apps out there, but they are all costly and I would prefer something that is both free and that I can use as data.  Please consider incorporating a fluency practice that could be used for both younger and older students who don't have their facts memorized.