NixOS
Declarative Linux distribution built on the Nix package manager. The entire system — packages, services, kernel, configuration — is described in a single file. The package manager computes the difference between current and desired state, making builds reproducible and rollbacks trivial.
Core properties
Reproducible. Packages are built in isolation with no undeclared dependencies. If a package works on one machine, it works on another.
Declarative. The user describes what the system should look like, not how to get there (xettel). The package manager handles the imperative path.
Reliable. Installing or upgrading one package cannot break others. Previous versions are always available for rollback.
Relevance to desired-state systems
NixOS is a canonical example of a desired-state system applied to operating system configuration. It wraps a mutable, imperative substrate (Linux) with a declarative interface — the pattern described by Jenco as the general shape of desired-state systems.