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.

Gerasimos Tsiamalos

Anastis Sourgoutsidis

Most of the “related posts” plugins out there while they provide some kind of control on how to create related posts, they all rely on an algorithm 
and the results are automatic. With CPTR you get total control as you can manually select the posts that you want to relate.

Custom Post Types Relationships (CPTR)

This plugin will let you create custom post relationships among posts, pages and custom post types.

tinyRelated vs Custom Post Types Relationships (CPTR)