This prototype is not available in the Google Play store, yet, so your phone will warn you about installing an app from an untrusted source. Once downloaded, find the file in your Downloads folder, then click on it. Android will step you through changing your settings to allow the installation. The app doesn't require any special privileges and makes no outgoing Internet connections.
Feedback is welcome! Please email Joe Winett at email@example.com.
Updated August 28, 2018