Viktor Androshuck

This lightweight plugin automatically scans the content of your posts and pages and adds <code>rel="nofollow noopener noreferrer"</code> to all external links. 
Internal links are untouched. Improves SEO and security with zero configuration.
<ul>
<li>No admin panel needed</li>
<li>Safe and fast</li>
<li>Does not affect internal links</li>
<li>Helps comply with SEO best practices</li>
</ul>

Auto External Link Nofollow


Does exactly what it says on the tin! No fluff, just "no follow" external links across your site 👍


Great Plugin

Automatically adds rel="nofollow noopener noreferrer" to all external links in post and page content.

cupcode

This plugin searches for words that you have specified and replaces them with other word or changes post status to draft, if found any of them.
You can choose between “Strict” and “Words Only” modes. If you choose “Strict” this plugins detects “able” in “Enable” and if you choose “Word Only” it detects “able” as a word and finds it a sentence like “Are you able to do this?”
This plugin searches for blacklisted words in post title, permalink, content and excerpt.

Post Filter

Post Filter allows you to replace all bad words with good ones in all post types with simple settings and easy to use interface.

Auto External Link Nofollow vs Post Filter