singpolyma

<ul>
<li>Detects tags from search engines, wikis, or other blogs</li>
<li>Auto-expands detected tags</li>
<li>Shows related posts based on tags</li>
<li>Provides JSON(P) feeds of tag results</li>
</ul>

FreshTags

Integrates FreshTags functionality into WordPress...

Marcus (aka @msykes)

Pixelite

Marcus

Meta Tags Manager is a powerful yet simple, lightweight plugin which allows you to add custom meta tags to your site. Features include:
<ul>
<li>Supports meta tags including the name, property, http-equiv, charset and itemprop attributes.</li>
<li>Choose from predefined types, such as ‘name=”keyword”‘ or create your own by typing it in.</li>
<li>Add meta tags to specific posts, choose what Custom Post Types to support from our settings page.</li>
<li>Add global meta tags that will display on specific CPTs, Taxonomies, your front page or your whole site.</li>
<li>Automatically add Open Graph details to your home page.</li>
<li>Automatically add Schema and Structured Data to your home page.</li>
<li>Add Google Sitelinks and Sitelinks Search markup.</li>
<li>Easily add verification codes for services like Facebook, Google Webmaster Tools, Bing Webmaster Tools, Yandex and more (or… create your own custom meta tags!).</li>
</ul>
Use cases include:
<ul>
<li>Adding Google and Yahoo site verification tags</li>
<li>Adding additional open graph, twitter card or other social media meta info not supported by other SEO/Meta plugins</li>
</ul>
<a href="https://metatagmanager.com/gopro/?utm_source=plugin-readme&utm_medium=plugin&utm_campaign=plugin" rel="nofollow ugc">Go Pro</a> for many newly added features, including:
<ul>
<li>Dynamic placeholders to include data about the page being displayed, such as page title, comment count, thumbnail URLs and more!</li>
<li>Additional contexts to add global meta tags, as well as exclusion rules for finer-grained controls.</li>
<li>Shortcode support within meta descriptions, allowing for more dynamic data insertion with plugins such as ACF</li>
<li>Unique tag detaction of Meta Tag Manager tags with hierarchical precedence, avoid creating duplicate meta tags.</li>
<li>Taxonomy support – create meta tags for individual taxonomy term pages such as a single tag or category.</li>
<li>More to come! Go Pro now and get an early-bird discount of up to 50%!</li>
</ul>

Meta Tag Manager

Easily add and manage custom meta tags to various parts of your site or on individual posts, such as Yahoo and Google verification tags.

FreshTags vs Meta Tag Manager