byronj

Easy Content Adder allows you to add custom content via a native WordPress editor and display the content at the top or bottom of all posts, pages, or both.
All text, links, and media attachments can be added to the custom content. If you can add it to a WordPress Page or Post, it can be added via Easy Content Adder.
<h3>Features</h3>
<ul>
<li>Hide the content from all posts without having to delete your content or disable the plugin.</li>
<li>Choose which post types to display the content on.</li>
<li>Display the content only on posts that have been tagged with select categories or taxonomies. </li>
<li>Chose whether to display the content at the bottom and/or top of all posts.</li>
</ul>

Easy Content Adder

A WordPress plugin to easily add custom content to all of your Pages, Posts, and Custom Post Types.

Amaury Balmer

Nicolas Juen

This plugin allow to build relation between 2 custom types (posts, page, custom), very useful for manage related content on CMS type website.
A few example use cases:
<ul>
<li>manually lists of related posts</li>
<li>post series</li>
<li>rented houses connected to agency</li>
<li>etc.</li>
</ul>
Relationships are created from a settings page from the administration console.
This plugin can not do relationships with users, you should test this excellent plugin made by scribu 
https://wordpress.org/extend/plugins/posts-to-posts/

Relations Post Types

This plugin allow to build relation between 2 custom types (posts, page, custom), very useful for manage related content on CMS type website.

Easy Content Adder vs Relations Post Types