Tran Ngoc Tuan Anh

This plugin adds rel=”nofollow” to all external links in post content. So, your flow of PageRank can not run to other websites and your blog’s SEO is improved.
The internal links are unchanged.
Requires PHP5.

External Nofollow

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.

External Nofollow vs External Links in New Window / New Tab