Devtard

<p>This plugin automatically searches posts when they are published/imported/saved and adds new taxonomy terms (<strong>tags</strong> by default) if term names or related keywords from a user-created keyword list are found.</p>
<h4>Features</h4>
<ul>
<li>Compatible with several post import plugins (<a href="https://wordpress.org/plugins/automatic-post-tagger/faq/" rel="ugc">FAQ #4</a>)</li>
<li>Supports <strong>custom taxonomies</strong> and <strong>post types</strong>; for example, APT is able to categorize posts (<a href="https://wordpress.org/plugins/automatic-post-tagger/faq/" rel="ugc">FAQ #6</a>), add tags/categories to WooCommerce products (<a href="https://wordpress.org/plugins/automatic-post-tagger/faq/" rel="ugc">FAQ #7</a>)</li>
<li>Supports <strong>UTF-8</strong> characters, non-Latin and logographic alphabets (<a href="https://wordpress.org/plugins/automatic-post-tagger/faq/" rel="ugc">FAQ #5</a>), including Arabic, Chinese, Cyrillic etc.</li>
<li>Bulk tagging tool (with a <strong>scheduler</strong>) for processing multiple posts</li>
<li>Import/Export tools (CSV & JSON format support)</li>
<li>Configuration groups with custom rules for selected keyword sets; wildcard (regex) support for related keywords</li>
</ul>
<p>See <a href="https://wordpress.org/plugins/automatic-post-tagger/screenshots/" rel="ugc">Screenshots</a> and <a href="https://wordpress.org/plugins/automatic-post-tagger/faq/" rel="ugc">FAQ</a> for more information.</p>


Automatic Post Tagger

Adds relevant taxonomy terms to posts using a keyword list provided by the user.

northswitch

<p>WP Full Auto Tags Manager automatically generate tags for all your blog posts, WP Full Auto Tags Manager is a free plugin for WordPress.<br />
You can auto tag all posts, create the tags automatically when publishing a post and or create automatically tags for untagged posts with scheduler.</p>
<h4>Features:</h4>
<ul>
<li>Auto Tag all posts</li>
<li>Clean all tags</li>
<li>Create the tags automatically when publishing a post</li>
<li>Create automatically tags for untagged posts every hour with scheduler</li>
</ul>
<span class="embed-youtube" style="text-align:center; display: block;"><iframe class="youtube-player" width="640" height="360" src="https://www.youtube.com/embed/B2nClgMw8r8?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation"></iframe></span>
<h4>Notification</h4>
<ul>
<li>This plugin uses a http://core.northswitch.org service to display updates and news notifications.</li>
</ul>
<h4>Visit:</h4>
<ul>
<li>http://core.northswitch.org</li>
</ul>


WP Full Auto Tags Manager

Thanks for this plugin, from all i have tested this works the best.
Please continue maintaining it!

Best autotaging plugin!

WP Full Auto Tags Manager automatically generate tags for all your blog posts.

Automatic Post Tagger vs WP Full Auto Tags Manager