Jeremy Shantz

I made this plugin to help with internal linking on existing sites, existing published content. 
Please feel free to donate if you like my plugin, it will help me feed my dogs and inspire me to add more functionality.
// Rest of your readme.txt file…
<h3>Usage</h3>
Here’s how it works:
You’ll find the plugin under the WordPress Settings menu.
Click on the plugin in the settings menu, and a user screen will appear where you can select (via dropdowns) either a single article or an article category target.
Next, you can select whether or not to include a link to your selected pillar post or page. If you choose Yes, select your preferred pillar post or page from the dropdown.
When you click the button to proceed, the plugin works as follows after selecting either a single article or a category.
a)The plugin will retrieve all the articles in the same category as either the single article you selected or the category you selected. 
b)The plugin will randomly select 6 articles in the same category and create an HTML heading and list of linked titles. It then adds this list to either the end of the single article or performs the same action on all articles in the category selected. 
c)If you selected Yes for pillar content, and you’ve selected the target post or page as the pillar, the plugin will proceed to add the title of your selected post or page as a bolded first item of the links list.
<h3>Donate</h3>
Support the development of this plugin by making a donation: https://www.paypal.com/donate/?hosted_button_id=RRN3SPBMJZT4G

Add Internal Links Lite

Add internal links to the end of a selected article's content or all articles in a selected category.

chrisguitarguy

agencypmg

SEO Auto Linker is an update to the much loved <a href="https://wordpress.org/extend/plugins/seo-automatic-links/" title="SEO Smart Links" rel="ugc">SEO Smart Links</a> plugin.
The plugin automatically links words and phrases in your post, page or custom post type content.
The difference is that you no longer have to try and guess what links will appear. Specify keywords in a comma separated list, type in the URL to which those keywords will link, specify how many links to the specified URL per post, and then specify the post type. SEO Auto Linker does the rest.
Bugs? Problems? <a href="http://pmg.co/contact" rel="nofollow ugc">Get in touch</a>.

SEO Auto Linker

I just recommended this to Paul Boag of the Boagworld podcast. It's that good that after 4 years since last update it's still working with a WordPress 4.8 I tested it on!

Very robust bit of kit

SEO Auto Linker allows you to automagically add links into your content. Great for internal linking!

Add Internal Links Lite vs SEO Auto Linker