OAK is a powerful kit of tools and components to use in your Android project (Compatible with API Level 8+)
OAK is licenced under Apache 2.0: that means it's free.
Have a look at the quick-start guide. Simply drop the jar into your android libs dir, or use your existing Ant or Maven2 build setup to auto-fetch sources and documentation, as well as bleeding edge snapshots.
OAK development is meant to be easy for Eclipse, IntelliJ, or Android Studio users. See the developer docs to see how you can make OAK even better.