Best for: Advanced runners or anyone who wants to lose body fat, boost speed, or improve overall fitness
Cool features: Most runners (or gym goers) are familiar with high-intensity interval training (HIIT) and its proven power to help increase speed and endurance. But rather than blindly poking at the treadmill console or constantly checking your watch, download this super-helpful app to stay focused on your footwork. Bit Timer, which promises to be the "World's Simplest Interval Timer Ever," has a clean and simple interface, making it easy to plug in your desired number of work periods, rest periods, and repetitions.
Available in the iTunes App Store