This is a hack that that allows you to swap internal storage with your external SD card so you can increase your app data storage.
All credits go to original i9300 App2ExtSD Hack by mattiadj. I simply hacked it to work with U.S. versions and also I’ve added code so it will disable this feature when you don’t have a microSD card inserted (app storage will default to internal when no microSD card is inserted).
E.g. If you have 16GB internal storage on Galaxy S3, you can install this witih a 64GB microSD card and swap the storage and get 64GB on your app storage instead of 16GB.