Stefano

When a post is saved, the plugin adds the rel=”nofollow” attributes to post external links. The plugin also provides an apt checkbox to exclude a post from plugin’s action.
Links which already have a rel attribute are just ignored, so you can set some dofollows are well.
By default, the plugin will only act on posts, no pages or other custom post types. To include (some of) them, use a code like the following, for ex. by putting it in your theme’s functions.php:
<pre><code>add_filter( 'rnf_post_types', function( $post_types ) {
 return array( 'post', 'page' ); #specify all desired CPTs, comma-separated
});
</code></pre>

Rel Nofollow

Adds rel="nofollow" to posts external links unless specified otherwise.

Nicki Faulk

This plugin marks all links in posts as ‘external’ and implements a small bit of javascript to open links in new windows. Inspired by Mdkart’s Add Lightbox plugin.

Blank Target Replacement

A target=_blank replacement using a small piece of javascript and rel=external.

Rel Nofollow vs Blank Target Replacement