GNU m4 - Development site
   René Seindal's site for developing the Free Software Foundation's version of the Unix macro processor.
   http://www.seindal.dk/rene/gnu/

m4
   Powerful (Turing-equivalent) implementation of traditional Unix macro-expansion program, designed as preprocessor to more stubborn languages. Ugly, but fairly standard, available on most platforms.
   http://www.gnu.org/software/m4/m4.html