I Googled to find the repository of a build system I wanted to mention and stumbled upon something else that I found interesting; https://shakebuild.com/
> Shake is a library for writing build systems. Most large projects have a custom-written build system, and developers working on the project are likely to run the build system many times a day, spending a noticeable amount of time waiting for the build system. This document explains why you might pick Shake over alternative tools for writing build systems (e.g. make, Ant, Scons).
Shake is written in Haskell and is open source.