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.

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.

Admin Documentation vs BuddyPress Docs