I made the quintessential amateur app using App Inventor (called Open Location). I had a need to make an Arduino “location aware” without a GPS module, so the app sends (via Bluetooth) a letter ‘A’ or ‘B’ depending if the user is within a user defined radius of a given coordinate . I wrote it for another project I was doing, and decided to throw it up on Play store for grins and giggles. I am actually re-writing it from scratch based on lessons learned, but still using AppInventor. There is certainly a performance hit and APK size penalty for using AppInventor but I got something working in a day vice weeks when I was trying to code in Eclipse.