Modern iPhones have become so massive that it’s becoming a challenge to operate them one-handed. For this reason, Apple implemented a feature in iOS called Reachability that pulls the contents of your display farther down so you can reach them with your thumb.
On any stock device, the Reachability interface leaves a large gap of unused space at the top of your display, but a new free jailbreak tweak called ReachIt by iOS developer Nepeta makes use of that wasted screen real estate by incorporating a Now Playing music interface into it.