Nix runs on Windows exactly like Docker runs on Windows— only inside a Linux VM. If you ship a Linux VM on Mac or Windows like people usually do for Docker, you're free to run the Linux version of a Nix package on those platforms.

> i.e. if a package depends on the systemd package https://search.nixos.org/packages?channel=unstable&show=syst... , Nix will not automatically find a replacement to run the package on Mac. But it may be possible to manually work around this with https://github.com/LnL7/nix-darwin

Nix-Darwin doesn't do anything for packaging issues, it just offers an alternative module system for declaratively managing services and configurations in a NixOS-like way.

Docker containers also don't normally do any kind of service management, they're single-process images. They're not really comparable to orchestrated services managed by NixOS or Nix-Darwin modules. But if your concern is just shipping the same thing and you don't care about what's managing the services, a whole NixOS VM isn't any less efficient than some other VM in which you run `docker-compose` or Kubernetes.

That said, there are Nix-y ways to ship one or more supervised processes in a way that's portable across the platforms that Nix supports. One way is with a manually tailored supervisord config with a nix-shell or something like devenv.sh. Another strategy would be to leverage something an abstraction layer like this one: https://github.com/svanderburg/nix-processmgmt