App Store. It's a product of the Belgian organization OVK, Parents of Children Killed in Road Accidents, and it has a very simple idea: if you drive too fast it slows down your music, as demonstrated below. Cross the limit and your thumping beats get run through molasses, but get back to a legal speed and Joanna Newsom's lilting highs stop sounding like a zombie's baleful lamentations. We're not entirely sure whether the app works outside of its native land at this point, and given how unreliable the indicated speed limits in navigation software tend to be we're not sure we want it to. But, if you have a bad habit you can't kick, this free app might just help.