FLTK (pronounced "fulltick") is a LGPL'd C++ graphical user interface
toolkit for X (UNIX), OpenGL, and Win32.  FLTK was designed to be small and
modular enough to be statically linked, but also works fine as a shared
library.  FLTK also includes FLUID, an interactive user interface builder
program.

This is version 1.3.  From the FLTK website:

  FLTK 1.3 is the current stable development branch based on FLTK
  1.1.10. It adds internationalization, UTF-8 (Unicode), and printing
  support, Doxygen based documentation, and several new widgets
  including Fl_Native_File_Chooser, Fl_Table, and Fl_Tree_View.

Homepage:
https://www.fltk.org/
