Amethyst Package Mounter (APM)
This is the core of Amethyst Linux's package management. It mounts a collection of packages as an overlay filesystem.
APM is written in C. Its only dependencies are a C library and the linux kernel headers. APM is linux-specific; it depends on kernel features including overlayfs, squashfs, and loop devices, so unless these features can be re-implemented for other kernels, or APM is modified to use similar features for other kernels, it will not be portable to other operating systems.
APM comes with documentation, athough it's not quite up to date with all the features I've added to it. One of my goals before I release a 1.0 version is to fully document all of those features, in a (hopefully) easy to understand way.
You can always download the latest version of APM from here. For historical purposes (e.g. if you want to see the process of making it), you can find older versions in the downloads directory. I would only recommend using the latest version.
Alternatively, if you're on Arch Linux or a derivative, you can build APM from source using makepkg with this PKGBUILD, or install it from my Arch Linux repository.
Note: For some weird reason, if you download it from firefox, civetweb is re-compressing the already-compressed tar.gz files. I don't know why this is, but for now you can work around it by decompressing it with gunzip twice. Alternatively, download it with wget or curl.