I think it's time for 2.0 version Mike...
I am getting tired of 1.x branch. There is FLTK v2.0 for SEVERAL YEARS! Mike, Bill, please let's start working on that! Pleaseeee!
It's a very nice GUI API Interface, much better than GTK I think. Documentation shourld be a better explan on EVENTs and other stuf.
Installation of FLTK
Make sure you have the Mesa Development source available. glx.h needs to be around or the source won't compile.
the documentation on the drawing functions
Documentation on the drawing functions (other than the GL widget which is very nicely explained in a batch of source code) is rather obscure in my opinion. The toolkit itself is a very good one and deserves to be absorbed in to wide use. Much better than GTK for rapidity of simple app development. As for complex apps I wouldn't know... yet.
An open, cross-platform journaling program.
A scientific plotting package.