The Purely Functional Linux Distribution
Popular configuration management systems have come a long way transforming imperative to declarative configuration. Rather than relying on extra tools that support a multitude of operating systems, NixOS is a GNU/Linux distribution with a novel take on both package and configuration management to achieve declarative and stateless service configurations on the operating system level.
NixOS includes Nix, a purely functional package manager, that provides isolation between multiple coexisting package versions, atomic upgrades & rollbacks, and runtime environments for package development. Think of tools like virtualenv or bundler but for all packages. NixOS leverages Nix to build stateless operating system environments based on purely functional Nix expressions. On hardware, in virtual machines or for containers. Multi-machine deployments of NixOS system configurations to a network or the cloud are realized with NixOps. With the capabilities of Nix/NixOS, NixOps enables atomic deployments and rollbacks of all machines defined in the configuration.