sammychen

This plugin will automatic add links to technorati tags or your blog’s tags where the words in your post match the tags of that post.
The most greatest things is that the plugin will not actually change your posts’ content in order to add links, so it will not hurt your posts. If you don’t want to use this plugin, just deactive it, and all links the plugin generated will automatic disapper just like they automatic come out, then your blog will return to its original status.
Go to Settings->Tag to Link for more information.
Rules Of Match 
Here are some rules when and how the convert take actions. These rules are only effective after version 0.5
<ol>
<li>If you tagged a post ‘hello world’ ‘hello’ ‘world’ and the content of your post is ‘hello world, I’m coming’, then this plugin will add link to ‘hello’, ‘world’, but not ‘hello world’, because there are links already. The rule can be simplily called Short Tag First.</li>
<li>If you tagged a post ‘hello world’ ‘hello’ ‘world’ and the content of your post is ‘bigworld, hellod, world’, then this plugin will add link to the last ‘world’, and no links will be added to ‘world’ of ‘bigworld’, or ‘hello’ of ‘hellod’.</li>
</ol>

Automatic Tag Link

This plugin will automatic add tag links to words in your content match the tag.

Bouzid Nazim Zitouni

PSMAN

TagGator lets you build a keyword list and apply matching tags to all your posts in one click.
How it works:
<ol>
<li>Enter your tag words in the Tag List — one per line, or comma-separated. Each word is both the tag name and the keyword searched for.</li>
<li>Configure matching options (case-sensitive, whole words, minimum occurrences).</li>
<li>Click Preview to see what would be tagged, or Bulk Tag All Posts to apply tags immediately.</li>
<li>Use Remove Unmatched Tags to clean up stale tags if you update your list.</li>
</ol>
Example tag list:
<pre><code>JavaScript, PHP, Python
WordPress, Gutenberg
Node.js, React, Vue
</code></pre>
A post containing “JavaScript” receives the “JavaScript” tag. Tags are only applied when the minimum match count is met, so you stay in control.
Features:
<ul>
<li>Flat tag list — every word is both tag and keyword, no complex syntax</li>
<li>Case-sensitive or case-insensitive matching</li>
<li>Whole-word or substring matching</li>
<li>Minimum match count in body and/or title</li>
<li>Enable/disable tagging per post type</li>
<li>Choose which taxonomy to tag with per post type</li>
<li>Preview before committing — no surprises</li>
<li>Remove Unmatched Tags cleans up only plugin-applied tags, never manually added ones</li>
<li>Tagging history in the post editor sidebar</li>
<li>No external dependencies, no tracking, no telemetry</li>
</ul>
Looking for more?
<a href="http://codecanyon.net/item/taggator-pro-wordpress-auto-tagging-plugin/1725033?ref=AngryByte" rel="nofollow ugc">[TagGator Pro]</a> adds:
<ul>
<li>Auto-tag posts on save — no manual bulk runs needed</li>
<li>Keyword-to-tag synonym mapping (one tag, many keywords per line)</li>
<li>Exclude posts by ID, category, or author</li>
<li>Per-post and per-user exclusion controls</li>
<li>Priority support</li>
</ul>

TagGator

Bulk-tag your posts by matching keywords against content. Simple, fast, and free.

Automatic Tag Link vs TagGator