Linux

Good question. NUR doesn't seem to output the packages directly, but requires that you supply your pkgs manually. You can use nix shell with NUR, but it gets rather ugly:

nix shell --impure --expr '(import (builtins.getFlake github:nix-community/NUR) { pkgs = (import  {}).pkgs; }).repos.mic92.hello-nur'

nix registry doesn't help here, as it's just for managing aliases that allow you to type "nixpkgs" instead of "github:NixOS/nixpkgs/nixos-23.05" in some places.

It might be possible to write a flake that outputs NUR packages for direct use, e.g. something like:

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.05";
    flake-utils.url = "github:numtide/flake-utils";
    nur_src.url = "github:nix-community/NUR";
  };

  outputs = { self, nixpkgs, flake-utils, nur_src }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
        nurpkgs = import "${nur_src}/default.nix" { pkgs = pkgs; nurpkgs = pkgs; };
      in {
        packages = nurpkgs.repos.mic92; // FIXME: this needs more work and filtering
      }
    );
}

Which gives:

$ nix --allow-import-from-derivation flake show .
git+file:///
└───packages
    ├───aarch64-darwin
    │   ├───bing-image-creator: package 'python3.10-bing-image-creator-0.4.4'
    │   ├───clearsans: package 'clearsans-1.00'
    │   ├───cntr: package 'cntr-1.5.1'
    │   ├───conky-symbols: package 'ConkySymbols'
    │   ├───eapol_test: package 'eapol_test-2.10'
    │   ├───edge-gpt: package 'python3.10-edge-gpt-0.13.1'
    │   ├───fira-code-pro-nerdfonts: package 'nerdfonts-3.0.1'
    │   ├───gatttool: package 'bluez-5.66'
    │   ├───gdb-dashboard: package 'gdb-dashboard-0.11.4'

But needs some more work and might be reinventing the wheel. Haven't used NUR myself and no idea what the state of flakes in NUR is.