add custom entries to menu options

Here a very quick example. The idea is to add a new meta box in the menu configuration. add_meta_box is used in admin_head-nav-menus.php page:

class Custom_Nav {
    function __construct() {
        add_action( 'admin_head-nav-menus.php', array( $this, 'add_nav_menu_meta_boxes' ) );
    }
    public function add_nav_menu_meta_boxes() {
        add_meta_box(
            'custom_links',
            __('Custom links'),
            array( $this, 'nav_menu_link'),
            'nav-menus',
            'side',
            'low'
        );
    }

    public function nav_menu_link() {?>
        <div id="posttype-custom-link" class="posttypediv">
            <div id="tabs-panel-custom-link" class="tabs-panel tabs-panel-active">
                <ul id ="custom-link-checklist" class="categorychecklist form-no-clear">
                    <li>
                        <label class="menu-item-title">
                            <input type="checkbox" class="menu-item-checkbox" name="menu-item[-1][menu-item-object-id]" value="-1"> <?php _e('Open entries', 'text-doamin'); ?>
                        </label>
                        <input type="hidden" class="menu-item-type" name="menu-item[-1][menu-item-type]" value="custom">
                        <input type="hidden" class="menu-item-title" name="menu-item[-1][menu-item-title]" value="<?php esc_attr_e('Open entries', 'text-doamin'); ?>">
                        <input type="hidden" class="menu-item-url" name="menu-item[-1][menu-item-url]" value="<?php echo esc_url( home_url('/open-entries') ); ?>">
                        <input type="hidden" class="menu-item-classes" name="menu-item[-1][menu-item-classes]" value="custom-link">
                    </li>
                </ul>
            </div>
            <p class="button-controls">
                <span class="add-to-menu">
                    <input type="submit" class="button-secondary submit-add-to-menu right" value="Add to Menu" name="add-post-type-menu-item" id="submit-posttype-custom-link">
                    <span class="spinner"></span>
                </span>
            </p>
        </div>
    <?php }
}

$custom_nav = new Custom_Nav;