Best Android Libraries You must have
android application development is not as easy as web based application but there are certain libraries and tools which can make you life easier described bellow
ActiveAndroid is a orm library which is very easy to use and configure make the development faster it can be downloaded from https://github.com/pardom/ActiveAndroid/
AndroidAnnotations is framework for android which can speed up the development process and help developer to focus on what is important instead of wasting time on none functional things more details on http://androidannotations.org/
Universal Image Loader is a library focused on image loading, caching and displaying.it is best for using with online assets. it can load images async and sync.can be found on https://github.com/nostra13/Android-Universal-Image-Loader
Fuel is a great library for the http protocol based networking as mostly of our applications are based on http so we must have it to faster our development https://github.com/kittinunf/Fuel
AndroidPdfViewer Library for displaying PDF documents on Android, with animations, gestures, zoom and double tap support. very easy to setup in project https://github.com/barteksc/AndroidPdfViewer
ZXing If you application involves QR code than you must use ZXing it is purely implemented in java so would be easier to configure https://github.com/zxing/zxing