Tom Belknap

The ultimate auto-tagging plugin for WordPress.
NOTE: The plugin is now being maintained on GitHub, so please do contribute all your questions, comments, suggestions, fixes and improvements with me <a href="https://github.com/holisticnetworking/title-to-terms" rel="nofollow ugc">here</a>.
Title to Terms Ultimate is for every WordPress admin that needs tags, categories and other taxonomies filled out automatically. For each post type in your WordPress installation, T2TU will allow you to assign a taxonomy to be automatically updated with keywords pulled from the title of the post.
Every time a post gets saved or updated, T2TU analyzes the title of the post for usable keywords. A list of user-configurable “Stop Words” is checked by the parser, so that words like “I” or “going” don’t get made into ultimately useless tags.
<ul>
<li>Converts keywords in post titles to terms in any taxonomy</li>
<li>Includes user-editable list of words to be ignored.</li>
<li>Ignore list can be reset to default at any time.</li>
<li>Converts on save, not publish.</li>
<li>Configurable to either add new terms or append the list of terms.</li>
</ul>
Multisite admins take note: this plugin is especially helpful if you’re building a community-based site where tagging is important and your bloggers are not always diligent about tagging.
<h3>Acknowledgements</h3>
<ul>
<li>The WP Plugin Repository icon and banner were both made with the kind contribution of: <a href="https://thenounproject.com/search/?q=taxonomy&i=165760" rel="nofollow ugc">Muharrem Fevzi Çelik @ The Noun Project</a> (CC licensed)</li>
</ul>

Title to Terms Ultimate

The ultimate auto-tagging plugin for WordPress.

chiefastro

Automatic Tags uses machine learning to automatically categorize and tag your posts.
Major features in Automatic Tags include:
<ul>
<li>Suggests tags for your post within the editor, in 3 different ways.
<ol>
<li>Existing tags mentioned in your post</li>
<li>Keywords mentioned in your post</li>
<li>Topics related to your post content</li>
</ol>
</li>
<li>Add all suggested tags with one click.</li>
<li>Suggests a category for your post within the editor.</li>
</ul>
Note: To get suggestions, you’ll need an API key from <a href="https://wpautotag.com" rel="nofollow ugc">wpautotag.com</a>. 
Keys are free and can be used on as many domains as you like. 
While editing posts, this plugin will send basic information about your post to the wpautotag.com API. The following information about your post is sent: post content, title, categories, tags, domain name, and (optionally) counts of how many posts you’ve published in each category. You can decline to send category counts by turning on the “blank slate” option on the settings page. 
Registering for an API key requires agreeing to the <a href="https://wpautotag.com/privacy-policy/" rel="nofollow ugc">privacy policy</a> and <a href="https://wpautotag.com/terms-of-use/" rel="nofollow ugc">terms of use</a> of wpautotag.com.

Automatic Tags

Automatically tag and categorize your posts.

Title to Terms Ultimate vs Automatic Tags