Appsly Android REST (AKA RESTrung) is a annotation based client library to connect to RESTful services on Android with an emphasis in simplicity and performance that automatically handles the implementation for most common REST use cases.
J2ObjC is an open-source command-line tool from Google that translates Java code to Objective-C for the iOS (iPhone/iPad) platform. This tool enables Java code to be part of an iOS application's build, as no editing of the generated files is necessary. The goal is to write an app's non-UI code (such as data access, or application logic) in Java, which is then shared by web apps (using GWT), Android apps, and iOS apps.
NexusDialog is a library that allows you to dynamically generate forms in Android with little code. It's great for apps with many form-based UIs, since it reduces the boilerplate code to setup the view layout and tie things together in the Activity.