Marcus Downing

When writing or modifying a theme, the function wp_nav_menu() displays the contents of menus configured in your settings. If you have a lot of little menus the list can get hard to manage, so this plugin lets you group several menus under a single menu.
To use it, simply add a <code>submenu</code> parameter to the arguments of wp_nav_menu, like so:
<pre><code>wp_nav_menu(array(
 'menu' => 'header',
 'submenu' => 'About Us'
));
</code></pre>

Subtitle Filter

Adds tha ability to show only a submenu with wp_nav_menu().

David Mosterd

Tobias Schutter

Uses the native <a href="https://codex.wordpress.org/Function_Reference/wp_nav_menu" rel="nofollow ugc">wp_nav_menu()</a>. Add parameters to the wp_nav_menu() to enable functionality. 
Also, ships with one-click delete menu-items in the WordPress admin. Turned off or on using the screen-options. Sweet.
Examples
This will get the first sub-menu from the active branch and 2 levels beyond (menu + sub-menu + sub-menu):
<pre><code>wp_nav_menu( array(
 'level' => 2,
 'depth' => 3
));
</code></pre>
Show the current branch only:
<pre><code>wp_nav_menu( array(
 'level' => 1
));
</code></pre>
Aimed on simple use in various use cases:
<pre><code>// display first level in the header
wp_nav_menu( array(
 'depth' => 1
));

// display first sub-menu from the current branch somewhere else
wp_nav_menu( array(
 'depth' => 2,
 'level' => 2
));
</code></pre>
Another feature is it’s control over the css classes that are given to a menu-item. You might be faced with css selectors 
which you cannot change. The ‘codepress_menu_filter_classes’ filter can be used in your functions.php to set the class property:
<pre><code>/**
 * Change the classes of a menu item
 *
 * @param array $classes List current classes
 * @param object $item Current menu item
 * @param array $items Current list of items (per level)
 * @param integer $k Key of the current item in $items
 */
function codepress_menu_item_classes( $classes, $item, $items, $k ) {
 // mark the first item
 if ( reset( $items ) == $items[ $k ] )
 $classes[] = 'first';

 // mark the last item
 if ( end( $items ) == $items[ $k ] )
 $classes[] = 'last';

 // map the WordPress default 'current-menu-item' class to 'active'
 if ( in_array( 'current-menu-item', $classes ) )
 $classes[] = 'active';

 return $classes;
}
add_filter( 'codepress_menu_item_classes', 'codepress_menu_item_classes', 10, 4 );
</code></pre>
Simple Menu Delete
It ships with one-click delete menu-items within WordPress. 
This functionality was integrated from our Simple Menu Delete plugin and enhanced a bit:
<ul>
<li>Turned off or on using the screen-options.</li>
<li>Display is more in line with WordPress’s way of delete-links.</li>
<li>Works exactly the same now as the nested delete-link which is a click further inside the menu item.</li>
</ul>

Codepress Menu

Allows you to display a sub-menu, it's depth from there on and gives you control over the menu-item classes.

Subtitle Filter vs Codepress Menu