The "Fast, Light Toolkit" (generally pronounced "fulltick")'s a cross-platform GUI library, developed by Bill Spitzak and others. Made with 3D graphics programming in mind, it's an interface to OpenGL, but it's still suitable for general GUI programming. Using its own widget, drawing and event systems (though FLTK2 has gained experimental support for optionally using the cairo graphics library) abstracted from the underlying system-dependent code, it allows for writing programs which look the s… (More on Fltk)