Redwoodcity

It is a plug-in that displays a notepad on the widget. The data is saved in LocalStorage in the browser, so you can use it easily without login.

WP Notepad

It is a plug-in that displays a notepad on the widget. The data is saved in LocalStorage in the browser, so you can use it easily without login.

wycks

Like a built in notepad, leave notes for clients or yourself in the WordPress admin. Attach notes to above or below the editor of a post (or page or custom post type) and also has a default “Notes” section available from the admin menu which you can hide or show.
The style of the notes section has been updated with the changes in WordPress 3.8+. Please note that the UI will not look great on WordPress version lower then 3.8 and there are no plans to fix this.
Features :
<ul>
<li>Uses WordPress’s built in custom post types</li>
<li>Functions with default WYSIWYG editor</li>
<li>Uses WordPress’s meta fields if set to display on post edit screens</li>
<li>Shows “Notes” on one page in tab format (can be excluded)</li>
<li>Will not show in front end or search</li>
<li>Requires default post privileges</li>
</ul>
Notes :
<ul>
<li>It is currently only possible to set one note per post and one location (above or below editor)</li>
<li>Works with password protection in default section</li>
</ul>
Please report issues to: <a href="https://github.com/wycks/Simple-Admin-Notes" rel="nofollow ugc">https://github.com/wycks/Simple-Admin-Notes</a>

Simple Admin Notes

Adds a simple "Notes" section to the admin menu or posts

WP Notepad vs Simple Admin Notes