The GNU Autoconf Archive is a collection of more than 500 macros for [GNU Autoconf](https://www.gnu.org/software/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.
* Noteworthy changes in release 2017.03.21 (2017-03-21) [stable] Obsolete macros AX_CXX_COMPILER_VENDOR, AX_GCC_LIBRARIES_DIR, AX_GCC_VERSION, and AX_HAVE_OPENGL have been removed from the archive. AX_DEFINE_SUB_PATH has been marked obsolete as suggested in https://github.com/peti/autoconf-archive/pull/97.