Lorna Timbah

Tag My Hash (#TagMyHash) is a lightweight WordPress plugin that bridges social-media-style hashtag usage with WordPress’s native tag taxonomy. This plugin scans your post content, identifies anything starting with a pound (a.k.a. hashtags sign #), and turns it into a functional part of your site’s tag structure. You no longer have to manually scroll down to the “Tags” meta box every time you want to categorise a quick update. A live front-end demo of this plugin can be found @ <a href="https://lornatimbah.com" rel="nofollow ugc">LornaTimbah.com</a>.
Features:
v.1.0: 
– Automatic hashtag detection in post content 
– Auto-create missing WordPress tags 
– Auto-assign hashtags as tags on save 
– Convert hashtags into clickable links to tag archive pages 
– Simple settings page (enable/disable + mode toggle) 
– Standard Posts support

Tag My Hash

Automatically converts #hashtags in your posts into WordPress tags and clickable links to tag archive pages.

fmzac

This plugin automatically converts keywords in a post title to tags upon saving. It includes a user-editable list of words you want the plugin to ignore, which by default includes the more obviously-useless words like “I” or “wasn’t.” You can also reset the list back to defaults by deleting/empty the current list.
<ul>
<li>Converts keywords in post titles to tags</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>Does not convert if there are already tags assigned.</li>
</ul>
Multi-blog adminstrators 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.

Auto Tag Generator

Automatically creates tags from post title, on update or publish.

Tag My Hash vs Auto Tag Generator