Not A Build System - Set of tools written with GNU Guile to make (semi-)auto-configurable Makefiles (requires GNU Make 4). No autotools, no CMake.
GNU Make 4.0 introduces the support for Guile. This allows for extremely powerful (thanks, Scheme!) scripting inside a Makefile. NABS is a set of Guile scripts meant to help create highly configurables Makefile while preserving the maintainer's sanity.
I started out with plain Makefiles, then embraced the autotools. Eventually I moved to CMake, and after a while ended up favoring plain Makefiles again.
Work in progress. You can't expect a final API right after the first commit.