My kingdom for a technology that lets me write an app once and run it acceptably on Android, iOS and in the browser. This probably beats everything else listed in this thread in terms of developer hours saved.
Are you aware of Apache Cordova? I've used it a couple times to deploy simple web apps as Android apps and I have no complaints about the result. Supports iOS also.
A vanilla web app. But you would still have issues designing for different screen sises, eg. someone with a 40 inch screen would be annoyed if the app was designed for 5 inch screens, and vice versa.
Just us out at [Ionic](https://ionicframework.com/) - a complete platform for doing just that. Write a web app using your framework of choice (or none at all!) then deploy as a PWA, iOS, Android, or Electron app.
