WebFactory

Opens external links in a new tab or a or new window. You can set URLs that should either be forced to open in a new window or ignored.
The plugin produces XHTML Strict compliant code and is search engine optimized (SEO). 
This is done using JavaScript’s <code>window.open()</code>-function. It adds only a few lines of vanilla JavaScript to the page, and does not require any external libraries like jQuery.
Most other plugins perform a hack by altering the <code>target</code> parameter (i.e. <code><a href="http://somewhere.example" target="_blank"></code>). That method is not XHTML Strict compliant. 
This plugin handles the links client-side, which lets search engines follow the links properly. Also, if a browser does not support JavaScript, the plugin is simply inactive, and does not result in any errors.
If you need a more advanced plugin, with more options try our <a href="https://wordpress.org/plugins/wp-external-links/" rel="ugc">free WP External Links</a> plugin.
Credits 
Inspired by the <a href="http://www.zappelfillip.de/2005-12-05/zap_newwindow/" rel="nofollow ugc">Zap_NewWindow</a> plugin by <a href="http://www.zappelfillip.de/" title="His website is mostly in German" rel="nofollow ugc">Tom Köhler</a>. 
The banner is a <a href="http://www.flickr.com/photos/monja/1367946568/in/photostream/" rel="nofollow ugc">photo</a> by <a href="http://www.monja.it/" rel="nofollow ugc">Monja Da Riva</a>.
Translations 
Danish by <a href="https://kristianrisagerlarsen.dk" rel="nofollow ugc">Kristian Risager Larsen</a> 
Dutch by <a href="http://www.collectief-it.nl/" rel="nofollow ugc">Paul Staring</a> 
Lithuanian by <a href="http://Host1Free.com" rel="nofollow ugc">Vincent G</a> 
Other translations will be appreciated!
Known bugs 
The plugin conflicts with other plugins that change the links’ `onClick´ attribute.
Original developer 
Kristian Risager Larsen – <a href="http://kezze.dk" rel="nofollow ugc">kezze.dk</a>

External Links in New Window / New Tab

Open external links in a new window or new tab. SEO optimized and XHTML Strict compliant.

Codious Technologies

Codious External Links Opener is a lightweight WordPress plugin that automatically opens all external links in a new browser tab. 
It also adds <code>rel="noopener noreferrer"</code> to external links for improved security and performance.
No setup required. Simply install and activate the plugin.
Features:
<ul>
<li>Automatically adds <code>target="_blank"</code> to external links</li>
<li>Adds <code>rel="noopener noreferrer"</code> for security and performance</li>
<li>No settings or configuration required</li>
<li>Lightweight and fast</li>
<li>Works with posts, pages, and custom post types</li>
</ul>
<h3>Credits</h3>
Developed by Codious Technologies

Codious External Links Opener

Automatically adds target="_blank" and rel="noopener noreferrer" to external links in post content to improve user experience and security.

External Links in New Window / New Tab vs Codious External Links Opener