Basecraft

Add a simple documentation page to your WordPress admin to keep instructions, notes, and other helpful information for maintaining your website.
<h4>Features</h4>
<ul>
<li>Create documentation using the WordPress content editor that you’re already familiar with.</li>
<li>Add text, images, videos, and other media to your documentation.</li>
<li>Organize your documentation into sections that automatically populate into a clickable table of contents.</li>
</ul>

Admin Documentation

Adds a simple documentation page to your WordPress admin to keep instructions, notes, and other helpful information for maintaining your website.

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.

Admin Documentation vs WPHelpKit