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.
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.
Well-designed widgets, coded with careful attention to rendering/execution speed.
FLTK code developed more than 10 years ago still compiles and runs perfectly, without changes.
Pro GUI designer
Fast Light User-Interface Designer (FLUID) included.
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.