William P. Davis

<p>This plugin will automatically links to terms in your content to that term’s page. Can be used for tags, categories and custom taxonomies. Based on Chen Ju’s Automatic Tag Links.</p>
<p>The plugin will only match full words, so if you have a term called “World” and use the word “worldwide” it will link not link world. Furthermore, if you have the term Worldwide Imports it will link the longer term first.</p>
<h3>Upcoming features</h3>
<ul>
<li>A better way to store terms in order to ensure better performance and more consistent linking.</li>
<li>Only link terms with more than x posts.</li>
</ul>


Terms to Links

This plugin will automatically link term names in your content to that term's detail page.

scribu

<p><strong>This plugin is outdated. Use <a href="https://wordpress.org/extend/plugins/term-management-tools/" rel="ugc">Term Management Tools</a> instead.</strong></p>


Merge Tags

Adds a new form on the tag management screen that lets you merge and replace tags and categories.

Terms to Links vs Merge Tags