Beat is a front-end for the music app and will playback any iTunes track on stored on your iPhone. The standout feature of Beat is its gesture controls. You can swipe, pinch, double tap and tap-hold to change views and control playback. When you launch the app for the first time, you are introduced to these various gesture controls. There's even a customizable shake option that allows you to shake your phone to play the next song, shake to play a random song, and more. Don't worry if you forget most of the gestures, they are in the settings under hints for you to review.
As someone who listens to music primarily while driving and running, the combination of gestures and shake are indispensable. I can use the gestures to easily swipe between songs without having to look at my phone to locate the forward and back button. The shake option while running works well as long as you are smooth with your arm motion. If you tend to be be jerky with your movement or fist pump, then the shake option will kick in. In these latter cases, you may want to turn the shake option off completely.
The seek option within Beat is also slick allowing you to tap and hold to bring up a scroll wheel. Sliding your finger up or down adjusts the playback head in one-second increments. The gesture is very responsive allowing you to find and start playing a song at any part of the track.
The best part about Beat is its price tag -- free. It's available for the iPhone and supports iOS 7.