Ryan Welcher

This is a simple plugin that helps to clean up the admin side of WordPress by only showing the currently logged in user’s content the Post/Page/Media pages.
For the Media list, you can provide a list of user ID’s who’s Media will also be available to logged in users. It is highly recommended to create a user for this purpose.
Credits
This plugin was inspired by an article by <a href="http://premium.wpmudev.org/blog/author/pollyplummer/" rel="nofollow ugc">Sarah Gooding</a> on <a href="http://premium.wpmudev.org/blog/how-to-limit-the-wordpres-posts-screen-to-only-show-authors-their-own-posts/" rel="nofollow ugc">wpmudev</a> and uses portions of that code. Please see the source code for further details.

Restrict User Content

Limits Post/Pages/Media admin screens to only display the current user's content. Media can be shared by providing an ID list.

scribu

AyeCode

Stiofan

Alex Ciobica

This plugin allows you to create many-to-many relationships between posts of any type: post, page, custom etc. A few example use cases:
<ul>
<li>manually curated lists of related posts</li>
<li>post series</li>
<li>products connected to retailers</li>
<li>etc.</li>
</ul>
Additionally, you can create many-to-many relationships between posts and users. So, you could also implement:
<ul>
<li>favorite posts of users</li>
<li>multiple authors per post</li>
<li>etc.</li>
</ul>
<h4>Support & Maintenance</h4>
AyeCode Ltd have committed to security and maintenance updates due to this plugins requirement in our <a href="https://wpgeodirectory.com/downloads/list-manager/" rel="nofollow ugc">List Manager Extension.</a>
~~I, scribu, will not be offering support (either free or paid) for this plugin anymore.~~
If you want to help maintain the plugin, fork it <a href="https://github.com/scribu/wp-posts-to-posts" rel="nofollow ugc">on github</a> and open pull requests.
Links: <a href="http://github.com/scribu/wp-posts-to-posts/wiki" rel="nofollow ugc">Documentation</a> | <a href="http://scribu.net/wordpress/posts-to-posts" rel="nofollow ugc">Plugin News</a> | <a href="http://scribu.net" rel="nofollow ugc">Author’s Site</a>

Posts 2 Posts

It works great. The options are beautiful, thought for every need, for example change a label or show only "to" box.

Works great

I'm working with WordPress, after some updates or actions the plugin starts to work incorrectly. The code is completely unreadable and can not be changed, the author abandoned his creation.
You can use - https://wordpress.org/plugins/npc-neatekpostconnect/

Huge load, unreadable code, Alternative for that plugin

Efficient many-to-many connections between posts, pages, custom post types, users.

Restrict User Content vs Posts 2 Posts