Brain training sounds like a mundane exercise, but a steady wave of sites and apps wants us to think of those words as anything but (we all know about this one). Each promises that you can improve your mental capacity in some way through a combination of puzzles and games.

Peak fits into this mold. The bright and colorful app has attracted a significant following over on Apple's mobile platform since its launch in September, with millions of downloads spread across two dozen countries.

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