Jonathan Bardo

Note: This plugin only works with WordPress 4.2 or higher
This plugin will enable the site administrator to easily create an admin message present on all pages. The admin has the option to let the user dismiss the message for the duration of his session.

Admin User Message

This does just what I want. Thanks for making it. :)
It's definitely better than https://wordpress.org/plugins/admin-screen-messages
You might want to also tag it as:
https://wordpress.org/plugins/tags/admin-message



Perfect

Add message to users of your site. Choose wheter they can dismiss it or not.

MB Creation

Popup a message on your WordPress blog is now very easy.
If you want to promote your brand new newsletter functionnality, display advertising on your homepage or get more Facebook fans you can use Simple Popup Manager to popup a message all over your content in a lovely “lightbox effect”. You can customize your message using a WP editor and of course specify the width and the height of the message box. You can limit the display of the message on either session or days basis.
<ul>
<li>Choose wether the popup will be displayed only on homepage or on every page</li>
<li>Set size, width and threshold of the popup (you can disable mobile)</li>
<li>Customize background-color and opacity</li>
<li>Popup content is just a normal WordPress editor (you can use shortcode)</li>
</ul>

Simple Popup Manager

Simple Popup Manager allows you to easily popup and display a simple message box on your WordPress front page.

Admin User Message vs Simple Popup Manager