Protocol Buffers are a way of encoding structured data in an efficient yet extensible format. Google uses Protocol Buffers for almost all of its internal RPC protocols and file formats.

A large library of pre-made animation effects for Android views.

All APIs for communicating with the Android system.

AndroidAsync is a low level network protocol library. If you are looking for an easy to use, higher level, Android aware, http request library, check out Ion (it is built on top of AndroidAsync). The typical Android app developer would probably be more interested in Ion. But if you're looking for a raw Socket, HTTP client/server, WebSocket, and Socket.IO library for Android, AndroidAsync is it.

Android Asynchronous Networking and Image Loading

A comprehensive library of pre-made android animation easing functions to help make animations appear more realistic.

VuDroid is a djvu and pdf document viewer based on code base of DjvuDroid and PdfDroid viewers.

A circular ImageView for Android applications.

The Facebook SDK for Android is the easiest way to integrate your Android app with Facebook's platform. The SDK provides support for Login with Facebook authentication, reading and writing to Facebook APIs and support for UI elements such as pickers and dialogs.

Build Realtime Apps. A powerful API to store and sync data in realtime.

The Google Analytics SDK for Android makes it easy for native Android developers to collect user engagement data from their applications. Developers can then use the Google Analytics reports to measure: The number of active users are using their applications. From where in the world the application is being used. Adoption and usage of specific features. Crashes and exceptions. In-app purchases and transactions. And many other useful metrics... The Google Analytics SDK also gives you the tools to monitor the success of mobile marketing campaigns. Connect user interactions with paid ads, Google Play downloads, and subsequent in-app usage and Ecommerce transactions. Google Analytics provides a powerful platform to measure and optimize all of your application marketing efforts.

Google Play services offers a standard authorization flow for all Google APIs and all components of Google Play services. In addition, you can leverage the authorization portion of the Google Play services SDK to gain authorization to services that are not yet supported in the Google Play services platform by using the access token to manually make API requests or using a client library provided by the service provider.