interfacelab

NOTE: This plugin requires PHP 7.1x or higher
The ILAB Docs plugin allows you to integrate help documentation for your WordPress theme or plugin directly 
into the WordPress admin.
Documentation is written in Markdown, with special extensions that make writing documentation in markdown easy. These 
extensions allow linking to other markdown files, linking to admin pages, video embeds, displaying a table of contents 
and other features. ILab Docs also has integrated search functionality for easily searching your documentation.
For examples integrating this documentation plugin with your plugin or theme, check out these examples:
<ul>
<li><a href="https://github.com/Interfacelab/ilab-docs-example-plugin" rel="nofollow ugc">Example plugin with documentation</a></li>
<li><a href="https://github.com/Interfacelab/ilab-docs-example-theme" rel="nofollow ugc">Example theme with documentation</a></li>
</ul>

WP Help Docs

Directly integrate markdown based help documentation for your WordPress theme or plugin into the WordPress admin for your end users and clients.

Boone Gorges

CUNY Academic Commons

David Cavins

BuddyPress Docs adds collaborative work spaces to your BuddyPress community. Part wiki, part document editing, part shared dropbox, think of these Docs as a BuddyPress version of the Docs service offered by the Big G ifyouknowwhatimean
Features include:
<ul>
<li>Docs that can be linked to groups or users, with a variety of privacy levels</li>
<li>Support for fully-private document uploads</li>
<li>Doc taxonomy, using tags</li>
<li>Fully sortable and filterable doc lists</li>
<li>TinyMCE front-end doc editing</li>
<li>One-editor-at-a-time prevention against overwrites, plus idle detection/autosave</li>
<li>Full access to revision history</li>
<li>Dashboard access and management of Docs for the site admin</li>
</ul>
This plugin is in active development. For feature requests and bug reports, visit http://github.com/boonebgorges/buddypress-docs. If you have translated the plugin and would like to provide your translation for distribution with BuddyPress Docs, please contact the plugin author.

BuddyPress Docs

I used it on a project for a client several years ago and it worked like a charm. Also, it was well-maintained.

WP Help Docs vs BuddyPress Docs