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The Android platform provides a number of ways to integrate your applications tightly into the operating system, enabling you to extend your reach beyond traditional application boundaries. In this chapter, you learned how to extend your application by creating App Widgets, live wallpapers, and more. The Android APIs provide many ways that applications can integrate into the system and take part in the user experience at many levels.
Android Dev Guide: “App Widgets”:
http://d.android.com/guide/topics/appwidgets/index.html
Android technical articles: “Live Wallpapers”:
http://d.android.com/resources/articles/live-wallpapers.html