Scott Reilly

This plugin removes the WordPress update nag that appears at the top of all admin pages when a new version of WordPress is released.
Tired of WordPress nagging you about a new release? Maybe you already know about it and want to hold off on an update and would rather not see the update nag on every admin page you visit. Activate this plugin and be bothered no more!
The status of your version of WordPress (be it current or out-of-date) is still reflected in the footer of your admin pages and in the update count link in the admin bar.
And certainly, of course, I don’t advocate completely ignoring the fact that updates often contain fixes for critical bugs or exploits. However, there are various other means of learning about updates; and once known, not everyone is able or willing to update immediately.
Links: <a href="https://coffee2code.com/wp-plugins/no-update-nag" rel="nofollow ugc">Plugin Homepage</a> | <a href="https://wordpress.org/plugins/no-update-nag/" rel="ugc">Plugin Directory Page</a> | <a href="https://github.com/coffee2code/no-update-nag/" rel="nofollow ugc">GitHub</a> | <a href="https://coffee2code.com" rel="nofollow ugc">Author Homepage</a>

No Update Nag

does what it says on the tin

Removes the WordPress update nag that appears at the top of all admin pages when a new version of WordPress is released.

Mat Gargano

Easily create, modify and manage popup notifications for your users. A modal is an effective way to draw attention to vital pieces of information. The Easy Nag Popup plugin makes popups a snap!
Acknowledgments: Serban Ghita (https://github.com/serbanghita) for Mobile-Detect and Marcus Westin (https://github.com/marcuswestin) for store.js.

Easy Nag Popup

Easily create, modify and manage popup notifications for your users. A modal is an effective way to draw attention to vital pieces of information.

No Update Nag vs Easy Nag Popup