App Inventor for Android is an application originally provided by Google and now maintained by the MIT, Massachusetts Institute of Technology. It allows anyone, including people unfamiliar with computer programming, to create software applications for the Android operating system. It uses a graphical interface, very similar to Scratch and the StarLogo TNG user interface, that allowes users to drag-and-drop visual objects to create an application that can run on the Android system, which runs on many mobile devices.
Easy to build the UI, then 1 click and you can start programming with "Code Blocks" that are super simple to use. You can then run it instantly with a downloadable emulator or just downloading the APK.