NUR (Nix User Repository) is a community package registry and distribution layer for Nix. In production it maintains a registry of several hundred user-contributed Nix repositories in repos.json, pins every entry to a specific revision in repos.json.lock, and exposes the aggregate as a Nix flake/overlay/package set. The Nix entry points (default.nix, flake.nix, lib/evalRepo.nix, lib/repoSource.nix) lazily translate locked registry entries into `nur.repos.<name>.<pkg>` attributes, including typed support for NixOS, Home Manager, Darwin, and flake-parts modules and overlays via flake-parts. The operational core is a small, typed Python CLI (`bin/nur` and `ci/nur/`) with subcommands for updating the lockfile, evaluating repos, formatting the manifest, generating a combined monorepo, and producing a search index. Updates run hourly via GitHub Actions: each repo is concurrently prefetched using either the Git smart HTTP protocol or GitHub/GitLab archive endpoints, evaluated in a sandboxed `nix-env` run to catch breakage, and then either locked to a new revision or pruned from the registry if deleted. A separate set of CI scripts publishes `nur-combined` and updates package search data. The architecture is cleanly split between Nix expression logic and Python automation, with careful handling of async concurrency, evaluation failures, and safety guards against accidental mass repository loss.