The current version of iCheckIn, a private app for use by Learning Tree instructors, was written in the Flutter SDK and both looks and behaves the same on both Android, and iOS. We could also make a desktop version (Windows, Linux, Mac) but there's already a web application for the non-mobile crowd.
Our founder, Ian Darwin, is the author of the O'Reilly Android Cookbook, containing advice from him and dozens of Android experts around the world on how to build great Android apps. He comes to Android from over a decade of building Java apps of all types: Swing, Web Server (Servlets, JSP, JSF, Seam 2, Java EE/Jakarta EE, ...), JavaME/BlackBerry, and more. Ian also wrote the O'Reilly Java Cookbook, now in its fourth edition, based on his experience with Java.
We have created many Android apps. Here are some that are in the Google Play Store: