DannyCooper

Enables a knowledge base post type and section taxonomy.
The plugin adds a Knowledge Base tab to your admin menu, which allows you to add articles just as you would regular posts. This allows you to keep your articles even if you change theme.
The Apollo Theme was built purposely to work with this plugin – <a href="http://crtv.mk/ez5P" title="Apollo WordPress Theme" rel="nofollow ugc">Apollo Theme</a>
<h4>Bugs</h4>
If you find an issue, let us know <a href="https://github.com/DannyCooper/knowledge-base-cpt/issues" rel="nofollow ugc">here</a>!
<h4>Contributions</h4>
Anyone is welcome to contribute to the Knowledge Base CPT plugin.
There are various ways you can contribute:
<ol>
<li>Raise an <a href="https://github.com/DannyCooper/knowledge-base-cpt/issues" rel="nofollow ugc">Issue</a> on GitHub</li>
<li>Send us a Pull Request with your bug fixes and/or new features</li>
<li>Translate the Knowledge Base CPT plugin into <a href="https://www.transifex.com/projects/p/knowledge-base-cpt/" rel="nofollow ugc">different languages</a></li>
<li>Provide feedback and suggestions on <a href="https://github.com/DannyCooper/knowledge-base-cpt/issues?direction=desc&labels=Enhancement&page=1&sort=created&state=open" rel="nofollow ugc">enhancements</a></li>
</ol>

Knowledge Base CPT

Enables a 'knowledge base post' type and 'section' taxonomy.

WP HelpKit

Create, Organize and Publish help content.
A simple tool for creating Knowledge Base and Documentation sites 
for your software products.
HelpKit for documentation sites 
is what WooCommerce is for eCommerce sites.
<h3>What can I do with HelpKit?</h3>
<ul>
<li>Help Center / Support Sites</li>
<li>Knowledge Base</li>
<li>Documentation</li>
<li>User Manuals</li>
<li>Wiki</li>
<li>FAQs</li>
</ul>

WPHelpKit

We've just started using it to document our WooCommerce themes and it seems to be exactly what we were looking for.

Exactly what we need

Create a fully featured Help Center site (Knowledge Base, Documentation, Wiki, FAQs) with WordPress.

Knowledge Base CPT vs WPHelpKit