
Flow - Library that helps with describing an app as a collection of moderately independent screens.
AndroidQuery - Android-Query (AQuery) is a light-weight library for doing asynchronous tasks and manipulating UI elements in Android.
AndroidStaggeredGrid - Grid view which supports multiple columns with rows of varying sizes. Cardslib - Android Library to build a UI Card. Pull to refresh - A swipe refresh layout is available in the v4 support library. Bubbles for Android - Facebook like chat bubble library. Audiogram - Lightweight audiowave progressbar. Timecon - Easy-to-use animated clock icon. Rajawali - Android OpenGL ES 2.0/3.0 Engine. Unity - Cross-platform game creation system. Libgdx - Cross-platform game engine and SDK. AndEngine - Free, Fun and Fast Android 2D OpenGL Game Engine. AndroidAnnotations - Java annotations with dependency injection at compile time. Butter Knife - View "injection" library for Android. Dagger 2 - A fast dependency injector for Android and Java. Dagger - Dependency injection framework for Java and Android. RoboGuice - Dependency injection framework for Android. Data Binding Library - Official Android Data Binding Library to write declarative layouts and minimize the glue code necessary to bind application logic and layouts. RoboBinding - A data-binding Presentation Model (MVVM) framework for the Android platform. Provides data binding and event listener binding, fits well for MVVM. Anvil - A small library to create reactive UI components, inspired by React. CloudRail - Unified API Library for: Cloud Storage, Social Profiles, Payment, Email, SMS & POIs. MPAndroidChart - An Android chart and graph library supporting scaling and dragging by gesture. HelloCharts - Chart and graph library with support for scaling, scrolling and animations. WilliamChart - Chart library with good motion capabilities. For general Java libraries have a look at awesome-java.
A curated list of awesome Android libraries and resources.