The iPhone 5 brought with it extra screen real estate, and Apple left it up to developers to optimize their apps to take advantage of the added space. Although many apps have been designed with the larger iPhone 5 display in mind, there are still some that have fallen through the cracks. Now with a jailbroken iPhone 5 and the FullForce for Phone tweak, you can stretch or expand these apps.
This means no more letterbox bars on the top and bottom of your iPhone 5 screen. FullForce knows which apps are not optimized to fill the screen, and will ask you what action to take the first time you run an app. Settings -> FullForce includes a list of apps and the behavior you want to take place when filling the iPhone 5 display.