DOS fork of FLTK
Mark Olesen recently announced his DOS fork of FLTK using Allegro4 and DJGPP. "fltkal is a DOS fork of the Fast Light Toolkit (FLTK) using Allegro4 and DJGPP. The fork required renaming files to 8.3 conventions. Other than that, however, the API is compatible with the 1.3.x and 1.4.x branch." You can see more at fltkal on Github.
This seems to be a separate effort than FLTK for DOS at SourceForge.