This is the LilyFN Fretboard Notator project, a custom LilyPond engraver for StaffTab(TM).

UPDATE: 
  I added the sample file "scheme-engraver.ly" from the LilyPond project.


Here's Carl Sorensen on getting started:

"Hmm -- how to get started?  Well, there are several things that you need to
figure out:

0) How to get the source with git.  It's really easy, especially if you use
the lily-git.tcl script.  See the Contributor's Guide for information.

1) How to write an engraver in Scheme.  Han-Wen just added that
functionality, and david pounder figured out how to use it.

See

http://thread.gmane.org/gmane.comp.gnu.lilypond.general/53740

for an example, and and see

http://thread.gmane.org/gmane.comp.gnu.lilypond.devel/26715

for Han-Wen's original explanation.

3) How to do the Scheme manipulation.  That's a bit harder for me to
explain.  I'd suggest you start with the Contributor's Guide chapter on
Programming.  Follow that up with the Scheme tutorial in Extending LilyPond.
Then try some stuff and see where you get stuck, and ask on the list for
help.  We'll be happy to provide it.

I hope this has been helpful.  I know it's a big chore to figure out how to
get started in LilyPond, but it's worth it!

Thanks,

Carl"