Keep your iDevice fast and free up RAM with this tweak.
Whenever you close an application on your device it stays open in the background for quick access later. The downside to this is the only way to truly close an application, and stop it using precious RAM, is to use the application switcher bar and kill the app yourself.
Auto App Killer helps your device run smoothly by automatically killing applications after you reach a certain amount of RAM space (which you set in the settings). Doing so will keep your device at or above this amount of RAM to ensure you have plenty of active memory for anything you do on your device.
This will NOT kill apps that are currently doing background processes (downloading something, playing music, receiving GPS information, VOIP, etc.). I.E. Pandora will NOT be killed if its playing music. This is done on purpose as to not ruin your experience while using your device.