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.

nathanlampe

The Bleep Filter plugin is a free and open source advanced content filtering plugin for WordPress. Commonly used as a bad word filter and swear filter, this plugin offers a variety of applications for your needs. Easily add the words you want to filter out and the plugin will find those words in your blog’s comments, posts, and rss feeds and passively replace them in a variety of styles.
Using a highly advanced phonetic algorithm, not only is the spelling being detected but also how the word sounds. This makes it much more difficult for mischievous posters to bypass the filter intentionally.
With the Bleep Filter plugin all you have to do is add your words and the plugin takes care of the rest.

Bleep Filter

An advanced word and content filter perfect for passively eliminating profanity and spoilers.

Auto External Link Nofollow vs Bleep Filter