There's NixOS, which you are describing, and then there's `nix` the package manager and build system. The latter is installable on any Linux or macOS system as

There's NixOS, which you are describing, and then there's `nix` the package manager and build system. The latter is installable on any Linux or macOS system as a normal binary, and can be used standalone as a build tool. My company uses this to standardize (and cache!) development environments across a diverse set of hardware; the environments do double-duty as hermetic CI builders as well.