A fast and lightweight C++ gui toolkit. There is no documentation available, but examples can be found on Erco's FLTK Cheat Page.
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It's simple design and lack of more advanced C++ features makes it easy for beginners.
Pro GUI designer
Fast Light User-Interface Designer (FLUID) included.
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 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.