fltk: fltk (C++ GUI toolkit) fltk: fltk: FLTK (pronounced fulltick) is a cross-platform C++ GUI toolkit for fltk: UNIX/Linux (X11), Microsoft Windows, and MacOS X. FLTK provides modern fltk: GUI functionality without the bloat and supports 3D graphics via fltk: OpenGL and its built-in GLUT emulation. fltk: fltk: fltk: fltk: fltk: