It is rare to come across apps for maths which don't adopt a schooly-type approach to teaching maths by hiding it rather badly in games which end up stiff and boring. Soooo when I came across DragonBox app I read some reviews first before purchasing the first one (DragonBox 5).
Here is a review on it - http://www.rudebaguette.com/2013/05/23/mathematics-learning-revolution-dragonbox-12/
I am definitely hooked. It takes a puzzle approach to teaching the abstract thinking skills of algebra. It has levels and 3 star ratings a bit like Angry Birds. As you advance through the levels, you learn the rules of the game (algebra) by either being told by the game at various points, or by intuitive reasoning eg. you get full stars if you solve/remove fractions first before continuing to problem solve the puzzles.
It is very deceptive : ) You start off playing with picture cards and getting them cancelled out and what is left over goes in this box. As the game progresses letters and numbers start creeping in with the pictures and because your brain is operating from picture puzzle solving, you just treat the numbers and letters the same way.
The kids and I are enjoying it and best of all, we get our own avatars, so our progress is saved under our separate avatars. No sharing of progress like we have to with Angry Birds! I'm glad I forked out the 6-7 dollars for the app, and will definitely pay 11 for the next - DragonBox 12 once we max 5 out.