Architecture Library

nucleus: an android library which utilizes the Model-View-Presenter pattern to properly connect background tasks with visual parts of an application.
mortar:A simple library that makes it easy to pair thin views with dedicated controllers, isolated from most of the vagaries of the Activity life cycle.
mosby
scoop: micro framework for building view based modular Android applications.
RxJava: a library for composing asynchronous and event-based programs using observable sequences for the Java VM.
dagger :A fast dependency injector for Android and Java

More to see