Arunas Liuiza

A tiny and simple hackable plugin to manually assign and display related posts. Incudes a widget, a shortcode (<code>[tinyrelated]</code>), a couple of template tags (<code>the_related_posts()/get_related_posts()</code>) for easy integration.
You can pick up to 10 related posts via a meta box in <code>Edit Post</code> window. If no posts were selected, there is an option to display random posts instead. Currently, there is no automatic generation of related posts.
The plugin is translation ready and has Lithuanian translation.
Also try out my other plugins:
<ul>
<li><a href="http://tiny.lt/gust" rel="nofollow ugc">Gust</a> – a Ghost-like admin panel for WordPress, featuring Markdown based split-view editor.</li>
<li><a href="http://tiny.lt/tinycoffee" rel="nofollow ugc">tinyCoffee</a> – a PayPal donations button with a twist. Ask people to treat you to a coffee/beer/etc. </li>
<li><a href="http://tiny.lt/tinytoc" rel="nofollow ugc">tinyTOC</a> – automatic Table of Contents, based on H1-H6 headings in post content.</li>
<li><a href="http://tiny.lt/tinyip" rel="nofollow ugc">tinyIP</a> – Premium – stop WordPress users from sharing login information, force users to be logged in only from one device at a time.</li>
</ul>
An enormous amount of coffee was consumed while developing these plugins, so if you like what you get, please consider treating me to a <a href="http://kava.tribuna.lt/en/" rel="nofollow ugc">cup</a>. Or two. Or ten.

tinyRelated

A tiny and simple plugin to manually assign and display related posts.

WebshopLogic

WP Related Posts and Products plugin offers different types of similar contents for your users. For example, some related products can be displayed to your similar posts. This makes connections of your site contents visible to your clients, increasing business efficiency.
Would you like to offer some related products to your blog posts? Do you need to offer up-sell or cross-sell products? Do you have an event calendar plugin, and want to suggest some programs connected to an article? Do you have a custom movie catalog plugin and want to associate some articles to your movies?
Using cross type relationship management functions, WRI makes it possible to associate a post, page, or other custom post type to other posts, pages or custom post types, ensures widely configurable relatedness settings, sophisticated cross-relation adjustments. WRI uses the most popular YARPP relationship handling plugin in the background, extending its functionality, retaining its advantages.
WRI combines automatic, manual and common categorization based relationship management. Some functions are available in the PRO version.
You can set attributes that define how to display different type of related items for every reference item type. Such a matrix-like way you can specify all necessary variations of display settings.
This version ensures built in WooCommerce custom product support.
<h4>More information, documentation</h4>
LITE: <a href="https://webshoplogic.com/products/wordpress_plugins/wp-related-posts-and-products-lite-plugin/#tab-faq&noscroll" rel="nofollow ugc">WP Related Posts and Products Lite Documentation</a> 
PRO: <a href="https://webshoplogic.com/products/wordpress_plugins/wp-related-posts-and-products-pro-plugin/#tab-faq&noscroll" rel="nofollow ugc">WP Related Posts and Products Pro Documentation</a>
<h4>Available languages</h4>
<ul>
<li>English</li>
<li>Spanish – translated by Andrew Kurtis – WebHostingHub </li>
<li>Hungarian – translated by WebshopLogic</li>
</ul>

WP Related Posts and Products (WRI)

WP Related Items plugin offers different types of similar contents for your users. For example, some related products can be displayed to your posts.

tinyRelated vs WP Related Posts and Products (WRI)