Nix is a family of deployment-related products, including a package manager, operating system (NixOS), continuous integration server (Hydra) and cloud deployment tool (NixOps). Almost all of our production servers are deployed using Nix.
So why pull a deployment tool into this discussion? Because setting up a development environment is essentially a deployment problem. Basically what you want is to deploy all the services, applications and libraries to your local machine so that you can start developing on a project.