This is one of the submodules used in Magisk. The project is licensed under GPL v3 (or newer). More info are written in the Magisk Main Repo
You need to install CMake and NDK to build the zipadjust library.
There are several files required to let Magisk Manager work properly, and they can be copied by using the build script in the Magisk Main Repo. These files are: magisk_uninstaller.sh, util_functions.sh, public.certificate.x509.pem, and private.key.pk8 under the app/src/main/assets folder.