Brain FLTK by Yaroslav Volovich
For designing parallel applications with FLTK toolkit.
FLTK Extensions by Alexey Parshin
SPDB library (ODBC library that was designed to work with FLTK), FLTK widgets, SPTK widgets library. [Open source, GPL]
GIDForums - FLTK Forum
FLTK toolkit discussions, including source code examples and tutorials. Example codes are syntax highlighted.
The vtkFLTK bridge library
A small C++ class library easing development of FLTK event-driven interfaces for use with VTK. vtkFLTK allows composition of complex graphical interfaces to complex visualization facilities by bridging disparities between FLTK and VTK event and windowing system handling. [Open source, BSD License]