{
  description = "Nixos configuration with flakes";
  inputs = {
    nixpkgs = {
      type = "github";
      owner = "NixOS";
      repo = "nixpkgs";
      ref = "nixos-21.05";
    };

    nixpkgs-unstable = {
      type = "github";
      owner = "NixOS";
      repo = "nixpkgs";
      ref = "nixos-unstable-small";
    };

    emacs-overlay = {
      type = "github";
      owner = "nix-community";
      repo = "emacs-overlay";
      ref = "master";
    };

    home-manager = {
      type = "github";
      owner = "nix-community";
      repo = "home-manager";
      ref = "release-21.05";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs = { self, nixpkgs, home-manager, ... } @inputs: {

    nixosConfigurations = {

      poseidon = nixpkgs.lib.nixosSystem rec {
        system = "x86_64-linux";
        modules = [
          ./poseidon.nix

          home-manager.nixosModules.home-manager
          {
            home-manager.useGlobalPkgs = true;
            home-manager.useUserPackages = true;
            home-manager.users.alarsyo = import ./home;
            home-manager.verbose = true;
          }

          {
            nixpkgs.overlays = [
              (self: super: {
                packages = import ./pkgs { pkgs = super; };

                # packages accessible through pkgs.unstable.package
                unstable = import inputs.nixpkgs-unstable {
                  inherit system;
                  config.allowUnfree = true;
                };

                fastPython3 = self.python3.override {
                  enableOptimizations = true;
                  reproducibleBuild = false;
                  self = self.fastPython3;
                  pythonAttr = "fastPython3";
                };

                matrix-synapse = super.matrix-synapse.override {
                  python3 = self.fastPython3;
                };
              })
            ];
          }
        ];
      };

      boreal = nixpkgs.lib.nixosSystem rec {
        system = "x86_64-linux";
        modules = [
          ./boreal.nix

          home-manager.nixosModules.home-manager
          {
            home-manager.useGlobalPkgs = true;
            home-manager.useUserPackages = true;
            home-manager.users.alarsyo = import ./home;
            home-manager.verbose = true;
          }

          {
            nixpkgs.overlays = [
              inputs.emacs-overlay.overlay

              (self: super: {
                packages = import ./pkgs { pkgs = super; };

                unstable = import inputs.nixpkgs-unstable {
                  inherit system;
                  config.allowUnfree = true;
                };

                steam = self.unstable.steam;
              })

              # uncomment this to build everything from scratch, fun but takes a
              # while
              #
              # (self: super: {
              #   stdenv = super.impureUseNativeOptimizations super.stdenv;
              # })
            ];
          }
        ];
      };

    };
  };
}