DrinkTracker Breathalyzer $1.99

With the amount of DUI and other alcohol related arrests constantly on the rise, and the penalties getting worse every year, it can't hurt to own this app. This app allows you to start a timer and add drinks as you go, letting you know your BAC. So when you can't always grab a cab, this app is the perfect tool to let you know if you're at risk of being above the legal limit.