diff --git a/README.md b/README.md
index 5097791..859d804 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,23 @@
 # services-flake
-NixOS-like services for Nix flakes
+
+NixOS-like services for Nix flakes, as a [process-compose-flake](https://github.com/Platonic-Systems/process-compose-flake) module (based on flake-parts).
+
+## Getting Started
+
+TODO
+
+## Services available
+
+- [x] Hello World
+- [-] PostgreSQL
+- [ ] MySQL
+- [ ] Redis
+- [ ] ...
+
+## Contributing
+
+We do not have CI yet, so please run `./test.sh` on **NixOS**.
+
+## Credits
+
+Thanks to [the devenv project](https://github.com/cachix/devenv/tree/main/src/modules/services) on which much of our services implementation is based on.
\ No newline at end of file
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..a0fc748
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,10 @@
+{
+  outputs = _: {
+    processComposeModules.default = ./nix;
+
+    templates.default = {
+      description = "Example flake using process-compose-flake";
+      path = builtins.path { path = ./example; filter = path: _: baseNameOf path == "flake.nix"; };
+    };
+  };
+}
diff --git a/nix/default.nix b/nix/default.nix
new file mode 100644
index 0000000..40f3bea
--- /dev/null
+++ b/nix/default.nix
@@ -0,0 +1,6 @@
+{
+  imports = [
+    ./hello.nix
+    ./postgres.nix
+  ];
+}
diff --git a/nix/hello.nix b/nix/hello.nix
new file mode 100644
index 0000000..068afcc
--- /dev/null
+++ b/nix/hello.nix
@@ -0,0 +1,24 @@
+{ pkgs, lib, config, ... }:
+
+{
+  options.services.hello = {
+    enable = lib.mkEnableOption "hello";
+    name = lib.mkOption {
+      type = lib.types.str;
+      default = "hello";
+      description = "Process name";
+    };
+    package = lib.mkPackageOption pkgs "hello" { };
+    greeting = lib.mkOption {
+      type = lib.types.str;
+      default = "Hello";
+      description = "The greeting to use";
+    };
+  };
+  config = let cfg = config.services.hello; in lib.mkIf cfg.enable {
+    settings.processes.${cfg.name}.command = ''
+      set -x
+      ${lib.getExe cfg.package} -g "${cfg.greeting}"
+    '';
+  };
+}
diff --git a/nix/postgres.nix b/nix/postgres.nix
new file mode 100644
index 0000000..d3af6ab
--- /dev/null
+++ b/nix/postgres.nix
@@ -0,0 +1,276 @@
+# Based on https://github.com/cachix/devenv/blob/main/src/modules/services/postgres.nix
+{ pkgs, lib, config, ... }:
+
+let
+  inherit (lib) types;
+in
+{
+  options.services.postgres = lib.mkOption {
+    description = ''
+      Enable postgresql server
+    '';
+    default = { };
+    type = lib.types.submodule ({ config, ... }: {
+      options = {
+        enable = lib.mkEnableOption "postgres";
+        name = lib.mkOption {
+          type = lib.types.str;
+          default = "postgres";
+          description = "Unique process name";
+        };
+
+        package = lib.mkPackageOption pkgs "postgresql" { };
+        extensions = lib.mkOption {
+          type = with types; nullOr (functionTo (listOf package));
+          default = null;
+          example = lib.literalExpression ''
+            extensions: [
+              extensions.pg_cron
+              extensions.postgis
+              extensions.timescaledb
+            ];
+          '';
+          description = ''
+            Additional PostgreSQL extensions to install.
+
+            The available extensions are:
+
+            ${lib.concatLines (builtins.map (x: "- " + x) (builtins.attrNames pkgs.postgresql.pkgs))}
+          '';
+        };
+
+        dataDir = lib.mkOption {
+          type = lib.types.str;
+          default = "./data/${config.name}";
+          description = "The DB data directory";
+        };
+        listen_addresses = lib.mkOption {
+          type = lib.types.str;
+          description = "Listen address";
+          default = "";
+          example = "127.0.0.1";
+        };
+
+        port = lib.mkOption {
+          type = lib.types.port;
+          default = 5432;
+          description = ''
+            The TCP port to accept connections.
+          '';
+        };
+
+        createDatabase = lib.mkOption {
+          type = types.bool;
+          default = true;
+          description = ''
+            Create a database named like current user on startup. Only applies when initialDatabases is an empty list.
+          '';
+        };
+
+        initdbArgs = lib.mkOption {
+          type = types.listOf types.lines;
+          default = [ "--locale=C" "--encoding=UTF8" ];
+          example = [ "--data-checksums" "--allow-group-access" ];
+          description = ''
+            Additional arguments passed to `initdb` during data dir
+            initialisation.
+          '';
+        };
+
+        settings = lib.mkOption {
+          type = with lib.types; attrsOf (oneOf [ bool float int str ]);
+          default = { };
+          description = ''
+            PostgreSQL configuration. Refer to
+            <https://www.postgresql.org/docs/11/config-setting.html#CONFIG-SETTING-CONFIGURATION-FILE>
+            for an overview of `postgresql.conf`.
+
+            String values will automatically be enclosed in single quotes. Single quotes will be
+            escaped with two single quotes as described by the upstream documentation linked above.
+          '';
+          default = {
+            listen_addresses = config.listen_addresses;
+            port = config.port;
+            unix_socket_directories = lib.mkDefault config.dataDir;
+          };
+          example = lib.literalExpression ''
+            {
+              log_connections = true;
+              log_statement = "all";
+              logging_collector = true
+              log_disconnections = true
+              log_destination = lib.mkForce "syslog";
+            }
+          '';
+        };
+
+        initialDatabases = lib.mkOption {
+          type = types.listOf (types.submodule {
+            options = {
+              name = lib.mkOption {
+                type = types.str;
+                description = ''
+                  The name of the database to create.
+                '';
+              };
+              schema = lib.mkOption {
+                type = types.nullOr types.path;
+                default = null;
+                description = ''
+                  The initial schema of the database; if null (the default),
+                  an empty database is created.
+                '';
+              };
+            };
+          });
+          default = [ ];
+          description = ''
+            List of database names and their initial schemas that should be used to create databases on the first startup
+            of Postgres. The schema attribute is optional: If not specified, an empty database is created.
+          '';
+          example = lib.literalExpression ''
+            [
+              {
+                name = "foodatabase";
+                schema = ./foodatabase.sql;
+              }
+              { name = "bardatabase"; }
+            ]
+          '';
+        };
+
+        initialScript = lib.mkOption {
+          type = types.nullOr types.str;
+          default = null;
+          description = ''
+            Initial SQL commands to run during database initialization. This can be multiple
+            SQL expressions separated by a semi-colon.
+          '';
+          example = lib.literalExpression ''
+            CREATE USER postgres SUPERUSER;
+            CREATE USER bar;
+          '';
+        };
+      };
+    });
+  };
+  config = let cfg = config.services.postgres; in lib.mkIf cfg.enable {
+    settings.processes =
+      let
+        postgresPkg =
+          if cfg.extensions != null then
+            if builtins.hasAttr "withPackages" cfg.package
+            then cfg.package.withPackages cfg.extensions
+            else
+              builtins.throw ''
+                Cannot add extensions to the PostgreSQL package.
+                `services.postgres.package` is missing the `withPackages` attribute. Did you already add extensions to the package?
+              ''
+          else cfg.package;
+      in
+      {
+        # DB initialization
+        "${cfg.name}-init".command =
+          let
+            setupInitialDatabases =
+              if cfg.initialDatabases != [ ] then
+                (lib.concatMapStrings
+                  (database: ''
+                    echo "Checking presence of database: ${database.name}"
+                    # Create initial databases
+                    dbAlreadyExists="$(
+                      echo "SELECT 1 as exists FROM pg_database WHERE datname = '${database.name}';" | \
+                      postgres --single -E postgres | \
+                      ${pkgs.gnugrep}/bin/grep -c 'exists = "1"' || true
+                    )"
+                    echo $dbAlreadyExists
+                    if [ 1 -ne "$dbAlreadyExists" ]; then
+                      echo "Creating database: ${database.name}"
+                      echo 'create database "${database.name}";' | postgres --single -E postgres
+
+
+                      ${lib.optionalString (database.schema != null) ''
+                      echo "Applying database schema on ${database.name}"
+                      if [ -f "${database.schema}" ]
+                      then
+                        echo "Running file ${database.schema}"
+                        ${pkgs.gawk}/bin/awk 'NF' "${database.schema}" | postgres --single -j -E ${database.name}
+                      elif [ -d "${database.schema}" ]
+                      then
+                        # Read sql files in version order. Apply one file
+                        # at a time to handle files where the last statement
+                        # doesn't end in a ;.
+                        ls -1v "${database.schema}"/*.sql | while read f ; do
+                          echo "Applying sql file: $f"
+                          ${pkgs.gawk}/bin/awk 'NF' "$f" | postgres --single -j -E ${database.name}
+                        done
+                      else
+                        echo "ERROR: Could not determine how to apply schema with ${database.schema}"
+                        exit 1
+                      fi
+                      ''}
+                    fi
+                  '')
+                  cfg.initialDatabases)
+              else
+                lib.optionalString cfg.createDatabase ''
+                  echo "CREATE DATABASE ''${USER:-$(id -nu)};" | postgres --single -E postgres '';
+
+            runInitialScript =
+              if cfg.initialScript != null then
+                ''
+                  echo "${cfg.initialScript}" | postgres --single -E postgres
+                ''
+              else
+                "";
+
+            toStr = value:
+              if true == value then
+                "yes"
+              else if false == value then
+                "no"
+              else if lib.isString value then
+                "'${lib.replaceStrings [ "'" ] [ "''" ] value}'"
+              else
+                toString value;
+
+            configFile = pkgs.writeText "postgresql.conf" (lib.concatStringsSep "\n"
+              (lib.mapAttrsToList (n: v: "${n} = ${toStr v}") cfg.settings));
+
+            setupScript = pkgs.writeShellScriptBin "setup-postgres" ''
+              set -euo pipefail
+              export PATH=${postgresPkg}/bin:${pkgs.coreutils}/bin
+
+              if [[ ! -d "$PGDATA" ]]; then
+                initdb ${lib.concatStringsSep " " cfg.initdbArgs}
+                ${setupInitialDatabases}
+
+                ${runInitialScript}
+              fi
+
+              # Setup config
+              cp ${configFile} "$PGDATA/postgresql.conf"
+            '';
+          in
+          ''
+            export PGDATA="${cfg.dataDir}"
+            ${lib.getExe setupScript}
+          '';
+
+        # DB process
+        ${cfg.name} = {
+          command = ''
+            set -x
+            export PATH="${postgresPkg}"/bin:$PATH
+            export LOCKDIR="/tmp"
+            postgres -k $LOCKDIR -D ${cfg.dataDir}
+          '';
+          depends_on."${cfg.name}-init".condition = "process_completed_successfully";
+          # SIGINT (= 2) for faster shutdown: https://www.postgresql.org/docs/current/server-shutdown.html
+          shutdown.signal = 2;
+          # https://github.com/F1bonacc1/process-compose#-auto-restart-if-not-healthy
+          availability.restart = "on_failure";
+        };
+      };
+  };
+}
diff --git a/nix/postgres_test.nix b/nix/postgres_test.nix
new file mode 100644
index 0000000..b2070e1
--- /dev/null
+++ b/nix/postgres_test.nix
@@ -0,0 +1,12 @@
+{ config, ... }: {
+  services.postgres = {
+    enable = true;
+    listen_addresses = "127.0.0.1";
+  };
+  testScript = ''
+    process_compose.wait_until(lambda procs:
+      procs["postgres"]["status"] == "Running"
+    )
+    machine.succeed("echo 'SELECT version();' | ${config.services.postgres.package}/bin/psql -h 127.0.0.1 -U tester")
+  '';
+}
diff --git a/test.sh b/test.sh
new file mode 100755
index 0000000..3aba908
--- /dev/null
+++ b/test.sh
@@ -0,0 +1,9 @@
+set -euxo pipefail
+
+cd "$(dirname "$0")"
+
+# On NixOS, run the VM tests to test runtime behaviour
+if command -v nixos-rebuild &> /dev/null; then
+  # service tests
+  nix flake check -L ./test
+fi
diff --git a/test/flake.lock b/test/flake.lock
new file mode 100644
index 0000000..029bc76
--- /dev/null
+++ b/test/flake.lock
@@ -0,0 +1,96 @@
+{
+  "nodes": {
+    "flake-parts": {
+      "inputs": {
+        "nixpkgs-lib": "nixpkgs-lib"
+      },
+      "locked": {
+        "lastModified": 1685662779,
+        "narHash": "sha256-cKDDciXGpMEjP1n6HlzKinN0H+oLmNpgeCTzYnsA2po=",
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "rev": "71fb97f0d875fd4de4994dfb849f2c75e17eb6c3",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1686089707,
+        "narHash": "sha256-LTNlJcru2qJ0XhlhG9Acp5KyjB774Pza3tRH0pKIb3o=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "af21c31b2a1ec5d361ed8050edd0303c31306397",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-lib": {
+      "locked": {
+        "dir": "lib",
+        "lastModified": 1685564631,
+        "narHash": "sha256-8ywr3AkblY4++3lIVxmrWZFzac7+f32ZEhH/A8pNscI=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "4f53efe34b3a8877ac923b9350c874e3dcd5dc0a",
+        "type": "github"
+      },
+      "original": {
+        "dir": "lib",
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "process-compose-flake": {
+      "locked": {
+        "lastModified": 1687194805,
+        "narHash": "sha256-DAqMJFWXft+eWrPOLWrP4xdK1DQELWkkU47PM+ODG2U=",
+        "owner": "Platonic-Systems",
+        "repo": "process-compose-flake",
+        "rev": "dd1dff00700deb2bc4afa44e7082c0176c095fd9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "Platonic-Systems",
+        "repo": "process-compose-flake",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-parts": "flake-parts",
+        "nixpkgs": "nixpkgs",
+        "process-compose-flake": "process-compose-flake",
+        "systems": "systems"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/test/flake.nix b/test/flake.nix
new file mode 100644
index 0000000..a6a2813
--- /dev/null
+++ b/test/flake.nix
@@ -0,0 +1,25 @@
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    systems.url = "github:nix-systems/default";
+    process-compose-flake.url = "github:Platonic-Systems/process-compose-flake";
+  };
+  outputs = inputs:
+    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = import inputs.systems;
+      imports = [
+        inputs.process-compose-flake.flakeModule
+      ];
+      perSystem = { self', pkgs, lib, ... }: {
+        process-compose = {
+          postgres = {
+            imports = [
+              inputs.process-compose-flake.processComposeModules.services
+              ../nix/postgres_test.nix
+            ];
+          };
+        };
+      };
+    };
+}