I’m sure you’ve had a need for something like this. While building WordPress–powered sites and blogs for other people, you sometimes need to provide some documentation for them to use the site correctly. A “style guide” is the first thing that comes to mind—like how authors should format their headlines as well as structure their post content. The WP Help plugin by Mark Jaquith solves problems like this, as described:
Administrators can create detailed, hierarchical documentation for the site’s authors and editors, viewable in the WordPress admin.
Now if you’re building a custom WP site with lots of customizations and tweaks, the WP Help plugin will make things easier for you and your users.