Android Unlocker Library : Library to Implement Unlock Application for Freemium Apps
Releasing a free version of your app and a paid version with more features is a common practice. This approach lets you publicize your app by providing them for free (hence possibly more downloads) with an option to monetize them with ads and at the same time you can also provide a better and feature rich version of the app to users who are willing to pay for the app. There are various different ways to implement distribution of such apps, with one most common ways being releasing an app with all the features for free but with the premium features locked, till the user purchase the app (and the premium features will be unlocked).
Android Unlocker Library provides a full system to help you develop Android applications that have a free version and some commercial unlocking application. It also offers the flexibility to implement multiple features to be unlocked by various unlocker applications.