It's a GNU Make framework which allows you to create non-recursive Makefiles. I've re-worked it a bit, and used it in my pet project: https://github.com/freeradius/freeradius-server/
100K+ LoC, ~400 source files, multiple subdirectories, building libraries, executables, etc.
Most of the slowness of Make is due to people creating recursive Makefiles. Running endless shell programs is very slow. Make by itself is surprisingly fast.
The other benefit of non-recursive Make is that the builds can now go in parallel. What used to be a ~90s build is now ~7s on a multi-core machine.
I also replace libtool (shudder) with jlibtool. That was taken from Apache, and modified to fix bugs work better, etc. That sped up the build a lot, too.
Maybe I'm crazy, but these tools have worked across all Unix-y platforms I've tried. And I needed a migration path from recursive Make / libtool to something better. Dropping the build system on the floor and hoping for something better wasn't an option. This tool suite works much like the old one, but it's simpler, faster, and doesn't require additional packages (python, etc.) to do the build. Everything outside of Make is self-contained, and is included in the FreeRADIUS distribution.
My projects:
https://github.com/alandekok/boilermake