Mom.vim is a project mainly written in Vim Script, it's free.
Syntax highlighting for the troff macro package
This is a mirror of http://www.vim.org/scripts/script.php?script_id=1231
Syntax highlighting for mom, a troff macro package, or as mom's homepage (http://faustus.dyn.ca/mom/mom.html) states: "mom is a typesetting and formatting package used to create high-quality, PostScript documents for printing."
This script is specialized for mom, although that is a troff macro package, this script does only have limited troff highlighting capabilities.