Nix OS is a Linux distribution where the system is configured using a functional programming language called Nix. Some of the advantages of this include:
easy to reproduce configs with options for many programs and services
a config will always do the same thing wherever it is moved to (no environment differences)
rollbacks of previous changes to configs, and old configs also appear in the boot-loader
changes can be tested without committing to them, or in a virtual machine
a source based package system with a cache so a specific package source only needs to be compiled once.
