Nix and NixOS
The package manager, language and operating system.
Nix is a package manager. It works on Mac, Windows (WSL2) and pretty much any Linux distro.
Nix is also a declarative expression language. You can use it to manage and configure web servers among other things.
NixOS is the Linux distribution that Shipnix uses on all servers.
NixOS is a Linux distribution built on top of the Nix package manager. It uses declarative configuration and allows reliable system upgrades.NixOS on Wikipedia
One benefit of NixOS is that you can manage you entire system configuration inside a git repo. Make your changes, push to git remote and rebuild the configuration.