Richard Venancio

This plugin used to get de sub menu refers the current item menu, and show this with a menu, for exemple a sub menu left.
Supose you have a big main menu, and this have a lot submenus, so, to show yours submenus in a side of your site, you create one new menu in wordpress for each submenu you have, and create codes to define which submenu you show, according the location in hierarchy’s menu you are.
This is very tiring and biggest, for just show the submenu, then this plugin do all things for you, but don’t create any menu, it just get the submenu according the main menu.

RVSubMenu

This plugin used to get de sub menu refers the current item menu, and show this with a menu, for exemple a sub menu left.

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.

RVSubMenu vs Codepress Menu