Aaron D. Campbell

There is a <a href="http://bluedogwebservices.com/problem-related-post-plugins/" rel="nofollow ugc">problem 
with related posts plugins</a>, and Efficient Related Posts is fixing that by 
approaching the problem from a different direction and offering a very different 
solution.
Basically, current related post plugins build the list of related posts on the 
fly when the user needs to view it. Since blogs tend to be viewed far more 
often than they are updated (often hundreds of times more often), these queries 
are run way more times than they need to be. This not only wastes CPU cycles, 
but if the queries are slow (which they will be if you have 1000s of posts and 
tags) then the user gets a poor experience from slow page loads.
Efficient Related Posts moves all this effort into the admin section, finding 
related posts when a post is saved rather than when the user views it. The 
advantage is that if the query is slow it happens less often and the post writer 
is the one that waits rather than the user (which I think is WAY better).
There are limitations. For example, since the related posts are stored as post 
meta data, we only store a certain number of them (10 by default, but you can 
set it to whatever you want). This means that if you decide you need to display 
more than 10, you need to have the plugin re-process all posts. I generally 
display up to 5 related posts, but store 10 just in case I decide to display 
more in some areas. Also, since the related posts are calculated when a post is 
saved, manually adding a tag through the database will have no effect on the 
related posts, although I recommend not doing that anyway.

Efficient Related Posts

A related posts plugin that works quickly even with thousands of posts and tags.  Can be added automatically to the end of posts.

Daniel Floeter

Mrinal Roy

Same Category Posts shows a list of related posts with a same Post Type to the current post. The widget is only shown on single post pages. Forked from <a href="https://wordpress.org/plugins/related-posts-widget" rel="ugc">Related Posts Widget</a>.
<h4>Tip Top Press</h4>
We’re <a href="http://tiptoppress.com/" rel="nofollow ugc">Tip Top Press</a> and create widgets for WordPress. If you want to know about what we’re working on and you are interested in backgrounds then you can read all newes storys on our <a href="http://tiptoppress.com/blog/?utm_source=wp.org&utm_medium=readme.txt&utm_campaign=same+category+posts" rel="nofollow ugc">blog</a>.
<h4>Features</h4>
<ul>
<li>Shows a list of related posts.</li>
<li>Option which Post Type should be related to the current post.</li>
<li>Custom Post Types support.</li>
<li>Child category and terms support.</li>
<li>Archive page support.</li>
<li>Option exclude one or multi categories or terms.</li>
<li>Option to filter by popular posts (by comment count).</li>
<li>Option <a href="http://tiptoppress.com/new-dynamic-layout-feature-separate-categories/" rel="nofollow ugc">separate categories</a> if more than one is assigned.</li>
<li>Set how many posts to show (overall and by category).</li>
<li>Option exclude current post, sticky posts or children.</li>
<li>Option exclude categories and terms without exclude their children.</li>
<li>Placeholders in title string (e.g. “There are a lot of %cat%-News.” -> “There are a lot of Tech-News.”).</li>
<li>Filter hook for the post titles ‘widget_title’.</li>
<li>Option to show post thumbnail and set width & height.</li>
<li>Option to <a href="http://tiptoppress.com/css-image-crop/" rel="nofollow ugc">crop thumbnails dimensions with CSS</a>.</li>
<li>Option to put thumbnail on top.</li>
<li>Option to make the widget title link to the category page.</li>
<li>Option to show/hide the title.</li>
<li>Option to show the post excerpt and how long (in words).</li>
<li>Option change excerpt ‘more’ text.</li>
<li>Option to show the post date, author and comment count.</li>
<li>Multiple widgets.</li>
</ul>
<h4>Placeholder</h4>
In text boxes %cat% will replaced with the (first assigned) category name, e.g. “There are a lot of %cat%-News.” -> “There are a lot of Tech-News.”
And %cat-all% will replaced with all assigned category name, e.g. “Special offers for %cat-all%!” -> “Special offers for houses, flats, apartments.”
<h4>Contribute</h4>
While using this plugin if you find any bug or any conflict, please submit an issue at 
<a href="https://github.com/DanielFloeter/same-category-posts" rel="nofollow ugc">Github</a> (If possible with a pull request).

Same Category Posts

Show posts related to the current category or other custom post types.

Efficient Related Posts vs Same Category Posts