Andrea Porotti

Using this plugin you can attach notes to some elements in the WordPress dashboard, such as:
<ul>
<li>posts</li>
<li>pages</li>
<li>custom post types from other plugins (except the notes from this plugin)</li>
<li>users</li>
<li>plugins</li>
<li>dashboard sections</li>
<li>the whole dashboard</li>
</ul>
It can be helpfull if you manage a site with other people or just to take notes for yourself.
Features
<ul>
<li>manage notes like the standard posts by opening the Notes page from the admin menu.</li>
<li>while editing a note, use the meta box on the right to set note properties (position, color,…)</li>
<li>manage section and global notes from the admin bar.</li>
<li>manage item notes (eg. posts and pages) from the custom column in the admin pages.</li>
<li>get notes details by hovering the mouse on the “Info” links or clicking on the “I” icons.</li>
<li>add text, images and links in the note content.</li>
<li>deleted notes go to the trash, so they can be restored.</li>
<li>automatically discovers custom post types added by other plugins (eg. events, books…).</li>
<li>creates a list of the dashboard sections based on the admin menu items.</li>
</ul>
Configuration
Settings for the plugin are available on the Settings -> JAMP Notes page.
Please note:
<ul>
<li>by default the plugin data is kept after uninstall. You can choose to delete notes and settings enabling the data removal option.</li>
<li>after activation, the plugin enables notes for all the existing public post types. If you then install other plugins which create new post types, you have to manually enable them in the JAMP settings.</li>
</ul>
Permissions
The notes are currently available only for the users with the “Administrator” role. 
Each Administrator can manage all notes.
Support
If you find any errors or compatibility issues with other plugins, please let me know in the support forum. Thanks!
Privacy
This plugin does not collect or store any user data. It does not set any cookies and it does not connect to any third-party services.

JAMP Notes (Just Another Memo Plugin)

This plugin allows you to attach notes to some WordPress elements like posts, pages, dashboard sections and more.

Michael Ott

Create admin text notes for any post, page or custom post type.
<h3>How To Use</h3>
<ul>
<li>Go to Settings -> Notely, choose which post types to enable for and any other options.</li>
<li>Hit the Save Settings button.</li>
<li>You will now see a Notes metabox when you create or edit.</li>
</ul>
<h3>Official website and support</h3>
<ul>
<li><a href="https://wordpress.org/support/plugin/notely" rel="ugc">Notely support</a></li>
<li>More options with <a href="https://rocketapps.com.au/product/notely-pro/?origin=notely" rel="nofollow ugc">Notely Pro</a></li>
<li><a href="https://rocketapps.com.au/shop/?origin=notely" rel="nofollow ugc">More awesome plugins</a></li>
<li><a href="https://rocketapps.com.au/wproject-theme/?origin=notely" rel="nofollow ugc">Project Management built on WordPress</a></li>
</ul>

Notely

Create admin text notes for any post, page or custom post type.

JAMP Notes (Just Another Memo Plugin) vs Notely