nix does not need nixOS to run but is a complex package manager. At least for me, it doesn't seem more complex than docker ecosystem.

I personally use nix to take care of downloading compatible dependencies in isolation for me. And the rest of the code is really, just basic script shell or Makefile too.

I also could add a fancy mergeShells function I have written in nix to support a docker-compose-like composition of nix-shell files. But you could go a very long way with nix before you even want to do something like this.