by Bohemia Plugins on WordPress.org
Create documentation for the site's authors, editors, and contributors viewable in the WordPress admin and avoid repeated "how-to" questions.

The Publishing Help screen, which lists and displays available help documents.
Site operators can create detailed, hierarchical documentation for the siteβs authors, editors, and contributors, viewable in the WordPress admin. Powered by Custom Post Types, you get all the power of WordPress to create, edit, and arrange your documentation. Perfect for customized client sites.
Highly inspired by the WP Help plugin, Help Manager provides the same functionality, up-to-date compatibility with WordPress, and brings some of the most requested features by its users.