The GNU Autoconf Archive is a collection of more than 450 macros for GNU Autoconf. They can be re-used without imposing any restrictions on the licensing of the generated configure script. In particular, it is possible to use them in configure scripts that are meant for non-free software.
Utterson is a static blog engine. It is based on a bunch of shell scripts and a self-generating makefile. Only basic Unix tools have been used (m4, GNU make, ksh93, rsync, ssh, etc.). It comes with emacs integration and support for mailing in blog posts automatically via procmail.
yuck is a command line option parser for C that works on a minimal set of dependencies - only a C compiler and the m4 macro processor are required. It supports all the standard use cases: GNU-style long options (--option), condensable short options (-xab for -x -a -b), and optional arguments to long and short options (--foo[=BAR]), multiple occurrence of options (-vvv). Most importantly, it does not depend on libc's getopt() nor getopt_long().