diff --git a/src/Core/Addon.php b/src/Core/Addon.php
new file mode 100644
index 0000000000..f9a21d429c
--- /dev/null
+++ b/src/Core/Addon.php
@@ -0,0 +1,300 @@
+<?php
+/**
+ * @file src/Core/Addon.php
+ */
+namespace Friendica\Core;
+
+use Friendica\App;
+use Friendica\Core\Config;
+use Friendica\Core\System;
+use Friendica\Database\DBM;
+
+/**
+ * Some functions to handle addons
+ */
+class Addon
+{
+    /**
+     * @brief uninstalls an addon.
+     *
+     * @param string $plugin name of the addon
+     * @return boolean
+     */
+    function uninstall_plugin($plugin) {
+        logger("Addons: uninstalling " . $plugin);
+        dba::delete('addon', ['name' => $plugin]);
+
+        @include_once('addon/' . $plugin . '/' . $plugin . '.php');
+        if (function_exists($plugin . '_uninstall')) {
+            $func = $plugin . '_uninstall';
+            $func();
+        }
+    }
+
+    /**
+     * @brief installs an addon.
+     *
+     * @param string $plugin name of the addon
+     * @return bool
+     */
+    function install_plugin($plugin) {
+        // silently fail if plugin was removed
+
+        if (!file_exists('addon/' . $plugin . '/' . $plugin . '.php')) {
+            return false;
+        }
+        logger("Addons: installing " . $plugin);
+        $t = @filemtime('addon/' . $plugin . '/' . $plugin . '.php');
+        @include_once('addon/' . $plugin . '/' . $plugin . '.php');
+        if (function_exists($plugin . '_install')) {
+            $func = $plugin . '_install';
+            $func();
+
+            $plugin_admin = (function_exists($plugin."_plugin_admin") ? 1 : 0);
+
+            dba::insert('addon', ['name' => $plugin, 'installed' => true,
+                        'timestamp' => $t, 'plugin_admin' => $plugin_admin]);
+
+            // we can add the following with the previous SQL
+            // once most site tables have been updated.
+            // This way the system won't fall over dead during the update.
+
+            if (file_exists('addon/' . $plugin . '/.hidden')) {
+                dba::update('addon', ['hidden' => true], ['name' => $plugin]);
+            }
+            return true;
+        } else {
+            logger("Addons: FAILED installing " . $plugin);
+            return false;
+        }
+    }
+
+    // reload all updated plugins
+
+    function reload_plugins() {
+        $plugins = Config::get('system', 'addon');
+        if (strlen($plugins)) {
+
+            $r = q("SELECT * FROM `addon` WHERE `installed` = 1");
+            if (DBM::is_result($r)) {
+                $installed = $r;
+            } else {
+                $installed = [];
+            }
+
+            $parr = explode(',',$plugins);
+
+            if (count($parr)) {
+                foreach ($parr as $pl) {
+
+                    $pl = trim($pl);
+
+                    $fname = 'addon/' . $pl . '/' . $pl . '.php';
+
+                    if (file_exists($fname)) {
+                        $t = @filemtime($fname);
+                        foreach ($installed as $i) {
+                            if (($i['name'] == $pl) && ($i['timestamp'] != $t)) {
+                                logger('Reloading plugin: ' . $i['name']);
+                                @include_once($fname);
+
+                                if (function_exists($pl . '_uninstall')) {
+                                    $func = $pl . '_uninstall';
+                                    $func();
+                                }
+                                if (function_exists($pl . '_install')) {
+                                    $func = $pl . '_install';
+                                    $func();
+                                }
+                                dba::update('addon', ['timestamp' => $t], ['id' => $i['id']]);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+    }
+
+    /**
+     * @brief check if addon is enabled
+     *
+     * @param string $plugin
+     * @return boolean
+     */
+    function plugin_enabled($plugin) {
+        return dba::exists('addon', ['installed' => true, 'name' => $plugin]);
+    }
+
+
+    /**
+     * @brief registers a hook.
+     *
+     * @param string $hook the name of the hook
+     * @param string $file the name of the file that hooks into
+     * @param string $function the name of the function that the hook will call
+     * @param int $priority A priority (defaults to 0)
+     * @return mixed|bool
+     */
+    function register_hook($hook, $file, $function, $priority=0) {
+        $condition = ['hook' => $hook, 'file' => $file, 'function' => $function];
+        $exists = dba::exists('hook', $condition);
+        if ($exists) {
+            return true;
+        }
+
+        $r = dba::insert('hook', ['hook' => $hook, 'file' => $file, 'function' => $function, 'priority' => $priority]);
+
+        return $r;
+    }
+
+    /**
+     * @brief unregisters a hook.
+     *
+     * @param string $hook the name of the hook
+     * @param string $file the name of the file that hooks into
+     * @param string $function the name of the function that the hook called
+     * @return array
+     */
+    function unregister_hook($hook, $file, $function) {
+        $condition = ['hook' => $hook, 'file' => $file, 'function' => $function];
+        $r = dba::delete('hook', $condition);
+        return $r;
+    }
+
+
+    function load_hooks() {
+        $a = get_app();
+        $a->hooks = [];
+        $r = dba::select('hook', ['hook', 'file', 'function'], [], ['order' => ['priority' => 'desc', 'file']]);
+
+        while ($rr = dba::fetch($r)) {
+            if (! array_key_exists($rr['hook'],$a->hooks)) {
+                $a->hooks[$rr['hook']] = [];
+            }
+            $a->hooks[$rr['hook']][] = [$rr['file'],$rr['function']];
+        }
+        dba::close($r);
+    }
+
+    /**
+     * @brief Calls a hook.
+     *
+     * Use this function when you want to be able to allow a hook to manipulate
+     * the provided data.
+     *
+     * @param string $name of the hook to call
+     * @param string|array &$data to transmit to the callback handler
+     */
+    function call_hooks($name, &$data = null)
+    {
+        $a = get_app();
+
+        if (is_array($a->hooks) && array_key_exists($name, $a->hooks)) {
+            foreach ($a->hooks[$name] as $hook) {
+                call_single_hook($a, $name, $hook, $data);
+            }
+        }
+    }
+
+    /**
+     * @brief Calls a single hook.
+     *
+     * @param string $name of the hook to call
+     * @param array $hook Hook data
+     * @param string|array &$data to transmit to the callback handler
+     */
+    function call_single_hook($a, $name, $hook, &$data = null) {
+        // Don't run a theme's hook if the user isn't using the theme
+        if (strpos($hook[0], 'view/theme/') !== false && strpos($hook[0], 'view/theme/'.current_theme()) === false)
+            return;
+
+        @include_once($hook[0]);
+        if (function_exists($hook[1])) {
+            $func = $hook[1];
+            $func($a, $data);
+        } else {
+            // remove orphan hooks
+            $condition = ['hook' => $name, 'file' => $hook[0], 'function' => $hook[1]];
+            dba::delete('hook', $condition);
+        }
+    }
+
+    //check if an app_menu hook exist for plugin $name.
+    //Return true if the plugin is an app
+    function plugin_is_app($name) {
+        $a = get_app();
+
+        if (is_array($a->hooks) && (array_key_exists('app_menu',$a->hooks))) {
+            foreach ($a->hooks['app_menu'] as $hook) {
+                if ($hook[0] == 'addon/'.$name.'/'.$name.'.php')
+                    return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * @brief Parse plugin comment in search of plugin infos.
+     *
+     * like
+     * \code
+     *...* Name: Plugin
+    *   * Description: A plugin which plugs in
+    * . * Version: 1.2.3
+    *   * Author: John <profile url>
+    *   * Author: Jane <email>
+    *   *
+    *  *\endcode
+    * @param string $plugin the name of the plugin
+    * @return array with the plugin information
+    */
+
+    function get_plugin_info($plugin) {
+
+        $a = get_app();
+
+        $info=[
+            'name' => $plugin,
+            'description' => "",
+            'author' => [],
+            'version' => "",
+            'status' => ""
+        ];
+
+        if (!is_file("addon/$plugin/$plugin.php")) return $info;
+
+        $stamp1 = microtime(true);
+        $f = file_get_contents("addon/$plugin/$plugin.php");
+        $a->save_timestamp($stamp1, "file");
+
+        $r = preg_match("|/\*.*\*/|msU", $f, $m);
+
+        if ($r) {
+            $ll = explode("\n", $m[0]);
+            foreach ( $ll as $l ) {
+                $l = trim($l,"\t\n\r */");
+                if ($l != "") {
+                    list($k,$v) = array_map("trim", explode(":",$l,2));
+                    $k= strtolower($k);
+                    if ($k == "author") {
+                        $r=preg_match("|([^<]+)<([^>]+)>|", $v, $m);
+                        if ($r) {
+                            $info['author'][] = ['name'=>$m[1], 'link'=>$m[2]];
+                        } else {
+                            $info['author'][] = ['name'=>$v];
+                        }
+                    } else {
+                        if (array_key_exists($k,$info)) {
+                            $info[$k]=$v;
+                        }
+                    }
+
+                }
+            }
+
+        }
+        return $info;
+    }
+}
diff --git a/src/Core/Theme.php b/src/Core/Theme.php
new file mode 100644
index 0000000000..f08d48efbc
--- /dev/null
+++ b/src/Core/Theme.php
@@ -0,0 +1,187 @@
+<?php
+/**
+ * @file src/Core/Theme.php
+ */
+namespace Friendica\Core;
+
+use Friendica\App;
+use Friendica\Core\Config;
+use Friendica\Core\System;
+use Friendica\Database\DBM;
+
+/**
+ * Some functions to handle themes
+ */
+class Theme
+{
+    /**
+     * @brief Parse theme comment in search of theme infos.
+     *
+     * like
+     * \code
+     * ..* Name: My Theme
+     *   * Description: My Cool Theme
+     * . * Version: 1.2.3
+     *   * Author: John <profile url>
+     *   * Maintainer: Jane <profile url>
+     *   *
+     * \endcode
+     * @param string $theme the name of the theme
+     * @return array
+     */
+
+    function get_theme_info($theme) {
+        $info=[
+            'name' => $theme,
+            'description' => "",
+            'author' => [],
+            'maintainer' => [],
+            'version' => "",
+            'credits' => "",
+            'experimental' => false,
+            'unsupported' => false
+        ];
+
+        if (file_exists("view/theme/$theme/experimental"))
+            $info['experimental'] = true;
+        if (file_exists("view/theme/$theme/unsupported"))
+            $info['unsupported'] = true;
+
+        if (!is_file("view/theme/$theme/theme.php")) return $info;
+
+        $a = get_app();
+        $stamp1 = microtime(true);
+        $f = file_get_contents("view/theme/$theme/theme.php");
+        $a->save_timestamp($stamp1, "file");
+
+        $r = preg_match("|/\*.*\*/|msU", $f, $m);
+
+        if ($r) {
+            $ll = explode("\n", $m[0]);
+            foreach ( $ll as $l ) {
+                $l = trim($l,"\t\n\r */");
+                if ($l != "") {
+                    list($k,$v) = array_map("trim", explode(":",$l,2));
+                    $k= strtolower($k);
+                    if ($k == "author") {
+
+                        $r=preg_match("|([^<]+)<([^>]+)>|", $v, $m);
+                        if ($r) {
+                            $info['author'][] = ['name'=>$m[1], 'link'=>$m[2]];
+                        } else {
+                            $info['author'][] = ['name'=>$v];
+                        }
+                    } elseif ($k == "maintainer") {
+                        $r=preg_match("|([^<]+)<([^>]+)>|", $v, $m);
+                        if ($r) {
+                            $info['maintainer'][] = ['name'=>$m[1], 'link'=>$m[2]];
+                        } else {
+                            $info['maintainer'][] = ['name'=>$v];
+                        }
+                    } else {
+                        if (array_key_exists($k,$info)) {
+                            $info[$k]=$v;
+                        }
+                    }
+
+                }
+            }
+
+        }
+        return $info;
+    }
+
+    /**
+     * @brief Returns the theme's screenshot.
+     *
+     * The screenshot is expected as view/theme/$theme/screenshot.[png|jpg].
+     *
+     * @param sring $theme The name of the theme
+     * @return string
+     */
+    function get_theme_screenshot($theme) {
+        $exts = ['.png','.jpg'];
+        foreach ($exts as $ext) {
+            if (file_exists('view/theme/' . $theme . '/screenshot' . $ext)) {
+                return(System::baseUrl() . '/view/theme/' . $theme . '/screenshot' . $ext);
+            }
+        }
+        return(System::baseUrl() . '/images/blank.png');
+    }
+
+    // install and uninstall theme
+    function uninstall_theme($theme) {
+        logger("Addons: uninstalling theme " . $theme);
+
+        include_once("view/theme/$theme/theme.php");
+        if (function_exists("{$theme}_uninstall")) {
+            $func = "{$theme}_uninstall";
+            $func();
+        }
+    }
+
+    function install_theme($theme) {
+        // silently fail if theme was removed
+
+        if (! file_exists("view/theme/$theme/theme.php")) {
+            return false;
+        }
+
+        logger("Addons: installing theme $theme");
+
+        include_once("view/theme/$theme/theme.php");
+
+        if (function_exists("{$theme}_install")) {
+            $func = "{$theme}_install";
+            $func();
+            return true;
+        } else {
+            logger("Addons: FAILED installing theme $theme");
+            return false;
+        }
+
+    }
+
+    /**
+     * @brief Get the full path to relevant theme files by filename
+     *
+     * This function search in the theme directory (and if not present in global theme directory)
+     * if there is a directory with the file extension and  for a file with the given
+     * filename.
+     *
+     * @param string $file Filename
+     * @param string $root Full root path
+     * @return string Path to the file or empty string if the file isn't found
+     */
+    function theme_include($file, $root = '') {
+        $file = basename($file);
+
+        // Make sure $root ends with a slash / if it's not blank
+        if ($root !== '' && $root[strlen($root)-1] !== '/') {
+            $root = $root . '/';
+        }
+        $theme_info = get_app()->theme_info;
+        if (is_array($theme_info) && array_key_exists('extends',$theme_info)) {
+            $parent = $theme_info['extends'];
+        } else {
+            $parent = 'NOPATH';
+        }
+        $theme = current_theme();
+        $thname = $theme;
+        $ext = substr($file,strrpos($file,'.')+1);
+        $paths = [
+            "{$root}view/theme/$thname/$ext/$file",
+            "{$root}view/theme/$parent/$ext/$file",
+            "{$root}view/$ext/$file",
+        ];
+        foreach ($paths as $p) {
+            // strpos() is faster than strstr when checking if one string is in another (http://php.net/manual/en/function.strstr.php)
+            if (strpos($p,'NOPATH') !== false) {
+                continue;
+            } elseif (file_exists($p)) {
+                return $p;
+            }
+        }
+        return '';
+    }
+}