You can get the plug-in and read its documentation here.
At some point in time, I wanted to display all posts in a category in my menu, without having to drag them there by hand every time. So I created a plug-in that would do that for me. Over time, I’ve extended it to support various parameters and options.
A short while ago, I managed to fix the remaining issues I had with the plugin, such as the custom fields not starting with an underscore _ and thus appearing in the custom fields for posts. That has been fixed now. Also, the plugin is now compatible with the wp_nav_menu_item_custom_fields hook that is not yet present in the WordPress core but allows multiple plugins to add fields to the Appearance > Menus page without causing conflict.
Lastly, the mechanisms I’m using in WordPress just seem a bit fragile. As it turns out it’s not possible to programmatically add posts to the menu and then programmatically give them children of their own. This makes adding the correct CSS classes quite a pain; although appears to work, I’ve reported an issue in the WordPress core where generation of CSS classes does not take into account plugins that remove, replace and add menu items via the wp_nav_menu_objects hook: https://core.trac.wordpress.org/ticket/32918
Regardless of this last issue, I hope users will find the plugin useful, I’m glad to see it still receives positive reviews and it’s being used quite a bit.