This looks like a really cool project. I downloaded the source and tried to build parts of it. I see references in some of the source to other applications, but wasn't sure where to find the source for those applications. For instance, flgames.cxx mentions flhangman, flfreecell, flpiano and some others. Where do you get the source for those programs?
Think this is a great idea and hope you'll continue to develop it.
Here's a list of some of the FLTK desktop applications I've experimented with building from source code and running:
https://lmemsm.dreamwidth.org/1565.html A few of them like fltdj might make useful additions to your office suite.