Add dev env

flake.nix

@@ -114,10 +114,37 @@
       } // machinesNodes;
 
       formatter = builtins.listToAttrs (
-        map (system: {
+        map (
+          system:
+          let
+            pkgs = import nixpkgsVersions.unstable { inherit system; };
+          in
+          {
             name = system;
-          value = nixpkgsVersions.unstable.legacyPackages.${system}.nixfmt-rfc-style;
+            value = pkgs.nixfmt-rfc-style;
-        }) flake-utils.lib.defaultSystems
+          }
+        ) flake-utils.lib.defaultSystems
+      );
+
+      devShells = builtins.listToAttrs (
+        map (
+          system:
+          let
+            pkgs = import nixpkgsVersions.unstable { inherit system; };
+          in
+          {
+            name = system;
+            value.default = pkgs.mkShell {
+              name = "Nix development environment";
+
+              packages = with pkgs; [
+                colmena
+                nixfmt-rfc-style
+                nil
+              ];
+            };
+          }
+        ) flake-utils.lib.defaultSystems
       );
     };
 }