Add nixosModules

all-modules.nix

@@ -6,6 +6,7 @@
     ./modules/devShell.nix
     ./modules/flake.nix
     ./modules/legacyPackages.nix
+    ./modules/nixosModules.nix
     ./modules/packages.nix
     ./modules/perSystem.nix
   ];

modules/nixosModules.nix

@@ -0,0 +1,27 @@
+{ config, self, lib, flake-modules-core-lib, ... }:
+let
+  inherit (lib)
+    filterAttrs
+    mapAttrs
+    mkOption
+    optionalAttrs
+    types
+    ;
+  inherit (flake-modules-core-lib)
+    mkSubmoduleOptions
+    ;
+in
+{
+  options = {
+    flake = mkSubmoduleOptions {
+      nixosModules = mkOption {
+        type = types.lazyAttrsOf types.unspecified;
+        default = { };
+        apply = mapAttrs (k: v: { _file = "${toString self.outPath}/flake.nix#nixosModules.${k}"; imports = [ v ]; });
+        description = ''
+          NixOS modules.
+        '';
+      };
+    };
+  };
+}