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.

GB071

ecreateinfotech

This plugin automatically converts keywords in a post/product title and category to tags upon saving. It includes a user-editable list of words you want the plugin to ignore
<ul>
<li>Converts keywords in post/product titles to tags</li>
<li>Converts keywords in post/product category to tags</li>
<li>Includes user-editable list of words to be ignored</li>
<li>Setting to enable for title and category separately</li>
<li>Setting to overwrite previous tag and consider only title and category while generating new one</li>
<li>Converts on publish and update.</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 Creator

Automatically creates tags from post/product title and category, on update or publish.

Tag My Hash vs Auto Tag Creator