When comparing NanoGUI vs Flutter, the Slant community recommends NanoGUI for most people. In the question“What are the best cross-platform GUI toolkits?” NanoGUI is ranked 4th while Flutter is ranked 15th. The most important reason people chose NanoGUI is:
Any control can be custom drawn.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Looks nice and it's easy to extend
Any control can be custom drawn.
Pro Open source
Pro Great developer tools debug/hotreload/analyser
Pro Based on Dart language
Dart is a Java like language, easy to learn and startup fast for millions of Java developers.
Pro A single codebase for iOS AND Android
Pro Fast
The developer's goal is to allow people to make apps running at 120 FPS.
Cons
Con Lacks a bunch of common widgets
Con Still in development
According to the website, Flutter is still in its early stages of development.
Con Based on Dart language
Dart is a Java like language, easy to learn and startup fast for millions of Java developers. BUT if you have to learn it ... it's a con.
Con Dart is unpopular and never gained serious community traction like Kotlin or Java
Con Does not support 32-bit iOS devices
If you plan on targeting iPhone 5, 5C or earlier, you can forget about Flutter.