Just watch the short video to see what this Cydia tweak does. In short, it allows you to make in app purchases for tons of apps for free. It doesn’t work for all apps, but there is lengthy list of apps listed for which it does. I believe it only works for iOS 5.0 and above which means it will not work on the iPad 2 or iPhone 4S until the jailbreak is released for these devices. This tweak can be found in the Xsellize or Insanelyi repos. If you don’t know how to add sources to Cydia you see how to add these two repos here.