xdark

Easy Related Posts is a WordPress plugin that displays posts related to the one a user is currently reading. 
Easy Related Posts can display related posts in main content area or in sidebars through a widget. 
Equipped with 3 eye catching fully responsive themes, supports basic modifications on them from admin panel. It also has a theme system that let you modify or write your own themes to match you personal needs. 
Through an intuitive algorithm it creates “relations” between posts and rates them based on posts categories and/or tags in a way so these ratings are as much as accurate they can be. 
Last but not least in any way, Easy Related Posts uses the best coding standards and practices with mind in security.
If you like this plugin please support the developers. You can do so using the links inside plugin settings page or by purchasing the PRO version.
PRO version can be purchased from <a href="http://erp.xdark.eu/downloads/easy-related-posts-pro/" rel="nofollow ugc">here</a>. 
To see a full list of features and compare them to the PRO version please visit <a href="http://erp.xdark.eu/version-comparison/" rel="nofollow ugc">this page</a>.
Easy Related Posts wont spam your visitors with content from other sites, ads or in any other way.
<a href="http://erp.xdark.eu/demo/" rel="nofollow ugc">See the demo</a>
This plugin requires PHP version 5.3 and above.
Features:
<ul>
<li>Easy to setup</li>
<li>Choose displayed content: excerpt length, thumbnail resizing and many more.</li>
<li>Choose if related posts should be fetched by categories or by tags</li>
<li>Exclude posts that have certain categories and/or tags from related posts</li>
<li>Prevent related posts from spawning in certain categories or tags</li>
<li>Display related posts as an eye-catching pop up block</li>
<li>Display related posts through a widget or/and in main content area</li>
<li>Options optimized before activation for most of the cases</li>
<li>Really fast, not a single database entry (I really love clean DB’s)</li>
<li>Responsive design</li>
</ul>
Please report any bugs or features you’d like to see in feature releases <a href="http://erp.xdark.eu/bugs/set_project.php?project_id=3" rel="nofollow ugc">here</a>

Easy Related Posts

Displays related posts in the end of each post or/and in sidebar through a widget

PickPlugins

Related Posts By PickPlugins plugin is one of the most useful plugin to display related post under post content on single post or page or custom post types, its also support to display related post under excerpt on archive pages. you can conditionally choose to display related content under excerpt or content by archive pages like tag, category, date, author, search page and custom taxonomy pages.
<h3>Related Post by http://pickplugins.com</h3>
<ul>
<li><a href="https://www.pickplugins.com/documentation/related-post/?ref=wordpress.org" rel="nofollow ugc">Documentation! »</a></li>
<li><a href="https://demo.pickplugins.com/related-post/?ref=wordpress.org" rel="nofollow ugc">Live Demo! »</a></li>
<li><a href="https://www.pickplugins.com/item/related-post-for-wordpress/?ref=wordpress.org" rel="nofollow ugc">Buy Pro! »</a></li>
</ul>
Tutorials
<ul>
<li><a href="https://www.youtube.com/watch?v=9SZKa0QYgsc" rel="nofollow ugc">How to install & setup</a></li>
</ul>
Related post under every paragraph
You can choose paragraph position like first, second, third and before last paragraph to display related post.
Before & After content and excerpt
Related post plugin allows you to display related content link before and after the content, this feature also available for excerpt under archive pages.
Related post under archive page
You can display related post under various archive pages like home page, front page, blog page, date, search, author, year, date, month and etc.
Related post by post types
You can choose custom post types to display Related post under single page.
Manual Post selection 
You can choose manually picked the post to display as related post for each post.
Advance query 
You can set max number post to display and choose query order and orderby parameters, related posts query based on current post category, tags and custom taxonomies.
Ready layout
There is 3 different type layout currently available to display related post, you can choose grid, slider and list style layout. you can set custom width for items and margin, padding, text align.
Sortable post elements
You can sort post elements like post title, post thumbnail and excerpt as you want.
Hide any elements
You can hide or display post elements like post title, thumbnail or excerpt.
Customize elements style
You can set custom font size, font color, padding, margin for post title, post excerpt and set custom height for post thumbnail, select custom thumbnail size and etc. you can also write custom CSS for each elements.
Track click
You can enable tracking click on related post, this will help you understand which post getting more attention from related posts. you will see top 10 post from stats page.
<h3>Premium Features</h3>
Popup related post 
You can display related post on popups under single blog post or custom post types,
Popup positions 
you can set 8 ready position for popups
Popup custom delay 
You can set custom delay to display popup, so popup will be hidden until certain amount of time and then it will display.
Popup display on scroll 
You can choose to display popup based on scroll down, popup will be hidden until certain amount of scroll down.
Popup display scroll down to article 
Popup will display when user scroll down to reached end of the article class or content.
Popup display scroll down to page 
Popup will display when user scroll down to reached end of the page or footer.
Custom HTML after each elements 
You can display custom HTML under each elements like post title, post excerpt and post thumbnails. you can also display 3rd party shrotcode as output after each elements.
Link Target 
You can set custom link target for each elements link like post title, post thumbnail and read more link, you can set _blank, _parent or etc for each link.
Display via shortcode
You can display related post any where via shortcode by using on your theme files
<pre><code><?php echo do_shortcode( '[related_post post_id=""]' ); ?>
</code></pre>

Easy Related Posts vs Related Posts By PickPlugins