Ranked in these QuestionsQuestion Ranking
It's simple design and lack of more advanced C++ features makes it easy for beginners.
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.
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.
Con Can be too simple for some projects
FLTK offers far fewer widgets than most other toolkits.