Codeko

With this plugin you can set any post type (or posts types) as parent of any post type.
Urls will be wellformed, redirects will work, breadcrumbs will work fine.
This plugin is recomended when you need a url structure with a mix of post types. Any url structure you can imagine could be done.
Post types rewrite slugs will be ignored

Custom Posts Parents

Set any post type (or types) as parent of any post type. Any post structure can be created with this plugin.

ambrosite

IMPORTANT: This plugin is not compatible with the Mystique theme, nor is it compatible with the WordPress 3.x custom menu system (that is, menus created using the drag-and-drop menu builder under Appearance->Menus). If you want to create an unlinked parent menu item with the Mystique theme, install Mark Jaquith’s ‘Page Links To’ plugin, and put a ‘#’ (hash/pound) mark in the ‘Point to this URL:’ field to create a dummy link. For the WP3 menu builder, use a ‘Custom Link’ with a ‘#’ mark in the URL field. Refer to the documentation in the WP Codex if you need more help: https://codex.wordpress.org/Appearance_Menus_Screen#Custom_Links
When activated, this plugin unlinks parent pages (that is, pages that have child pages underneath them in a hierarchy) in page menus and lists. It affects the output of wp_list_pages and wp_page_menu, as well as all plugins and widgets that use those functions.
The plugin works by turning the parent page links into ‘dummy links’. That is, it replaces the href attribute on parent menu items with a ‘#’ (hash/pound) mark. A dummy link is just like a regular link, except that it leads back to the current page when clicked. The dummy links are given an inline style “cursor: default” to prevent the mouse pointer from turning into a hand when hovering over unlinked menu items.
<h4>Options</h4>
To configure the plugin options, go to the Settings menu in the WordPress admin panel and click on ‘Unlink Parent Pages’.
Use Dummy Links 
Turned on by default as of Unlink Parent Pages version 1.3. If you uncheck this box, the plugin will unlink the parent pages by replacing the anchor tags with span tags. In some themes, this may cause problems with CSS styling. In order to fix this, you would need to add an additional selector to any rule that targets the anchor tags (see the FAQ for more information). If you are not experienced in writing CSS selectors, then it is strongly recommended to stick with dummy links.
Unlink Current Page 
Unlink the current page, in addition to the parent pages.
Remove Link Titles 
Remove the title attribute from the links (stops the tooltip from popping up when the mouse hovers over the menu items). This doesn’t have anything to do with unlinking parent pages, but it’s something a lot of people want, so I decided to include it.
Maximum Depth 
The maximum depth setting controls how many levels in the hierarchy of pages are to be unlinked. It works exactly like the ‘depth’ option for wp_list_pages, as follows:
<ul>
<li>0 (default) Unlinks all parent pages, anywhere in the page hierarchy.</li>
<li>1 Unlinks top-level parent pages only.</li>
<li>2, 3, … Unlinks parent pages to the given depth.</li>
<li>-1 Do not unlink any pages (specify individual pages instead).</li>
</ul>
Unlink Specific Pages 
You can specify which pages you want unlinked, using a comma-separated list of page IDs (example: 3,7,31). It works exactly like the ‘exclude’ option for wp_list_pages. If you want only the specified pages to be unlinked, then set max depth to -1.

Ambrosite Unlink Parent Pages

Unlinks parent pages in page menus and lists. Useful for creating dropdown menus with top-level placeholders. Affects the output of wp_list_pages and  …

Custom Posts Parents vs Ambrosite Unlink Parent Pages