I recommend The Flutter Framework from Google to anyone who wants to create simple mobile apps for iOS and Android at the same time. The code is written in Dart, then it is compilable for iOS and Android. Flutter and Dart is still very young and is being further developed by Google.
The iOS app will then compiled via CocoaPods and Android will recognize the programming language Dart. Flutter uses widgets and everything is written and coded in widgets.
As an iOS Developer, I wanted to think outside the box and am satisfied with the Flutter Framework. Of course, the framework still shows limits, since it is still so young. Nevertheless I have to take the hat off to the Flutter development team, because they have done a good job so far.