The GNU Autoconf Archive is a collection of more than 450 macros for `GNU
Autoconf` that have been contributed as free software by friendly supporters
of the cause from all over the Internet. Every single one of those macros
can be re-used without imposing any restrictions whatsoever on the licensing
of the generated 'configure' script. In particular, it is possible to use
all those macros in `configure` scripts that are meant for non-free
software. This policy is unusual for a Free Software Foundation project.
The FSF firmly believes that software ought to be free, and software
licenses like the GPL are specifically designed to ensure that derivative
work based on free software must be free as well. In case of Autoconf,
however, an exception has been made, because Autoconf is at such a pivotal
position in the software development tool chain that the benefits from
having this tool available as widely as possible outweigh the disadvantage
that some authors may choose to use it, too, for proprietary software.