Sajidul Islam

This is a simple plugin- Which will allow you to add instruction for the individual post types like- page, post etc.

Dashboard Instruction Guide

This is a simple plugin- Which will allow you to add instruction for the individual post types like- page, post etc.

VDmitryV

This plugin allows developers to use the WordPress WYSIWYG editor for their own 
fields during plugin/theme development, for example – for Custom Post Types. 
Code is based on WordPress the_editor code.
Sponsored by GlobalBases.com GmbH WebBases & WebSoftware http://www.globalbases.com
PLEASE NOTE: Plugin is in alpha stage of development, so don’t expect it to be fully working. Don’t expect anything.
Known limitations: working only on post create/edit pages

WYSIWYG Helper

Plugin for developers that want to use WYISIWYG in their plugins/themes.

Dashboard Instruction Guide vs WYSIWYG Helper