When comparing Fyne vs FLTK, the Slant community recommends FLTK for most people. In the question“What are the best cross-platform GUI toolkits?” FLTK is ranked 12th while Fyne is ranked 24th. The most important reason people chose FLTK is:
It's simple design and lack of more advanced C++ features makes it easy for beginners.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Mobile support
Android and iOS are supported.
Pro Easy to learn
Simple and consistent API.
Pro Permissively licensed
Fyne is licensed under the 3-clause BSD license, which has fairly lax restrictions on usage.
Pro Simplicity
It's simple design and lack of more advanced C++ features makes it easy for beginners.
Pro Fast
Well-designed widgets, coded with careful attention to rendering/execution speed.
Pro Stable
FLTK code developed more than 10 years ago still compiles and runs perfectly, without changes.
Pro Lightweight
Uses a limited and lightweight design and restricts itself to solely GUI functionality. Because of this restriction, the FLTK hello world example is only about 100 KiB.
Pro GUI designer
Fast Light User-Interface Designer (FLUID) included.
Cons
Con Go specific
Fyne is only usable in Go applications.
Con Can be too simple for some projects
FLTK offers far fewer widgets than most other toolkits.
Con Does not look like a native application
Because it uses non-native widgets, it doesn't look like a native application on any platform.
