Markus Echterhoff

This plugin is as simple as it is useful. Add the widget or use the shortcode <code>[you-have-a-new-message]</code> anywhere to display a notice if the currently logged in user has new messages. The notice links to the user’s inbox as a convenient and omnipresent shortcut.
Message texts can be configured via widget interface and shortcode parameters, e.g. <code>[you-have-a-new-message single="new message" multiple="%s new messages"]</code>.
<h4>Translations:</h4>
<ul>
<li>German</li>
</ul>

You Have a New (BuddyPress) Message

Notify users about new BuddyPress messages (widget & shortcode)

Apsara Aruna

This is popup simple message on you all pages or specific page.
Features 
*Show popup alert on specific pages.
Also see my other plugins 
* <a href="https://wordpress.org/plugins/widget-youtube-subscribtion/" title="Easy Subscribe Button Widget" rel="ugc">Easy Subscribe Button Widget</a> 
* <a href="https://wordpress.org/plugins/embed-page-facebook/" title="Easy Embed Page Widget" rel="ugc">Easy Embed Page Widget</a>
Special Thanks for 
* <a href="https://codeseven.github.io/toastr/" title="Toastr Simple javascript toast notifications" rel="nofollow ugc">Toastr</a>

Toast Popup Notification News Alert

This is popup simple message on you all pages or specific page.

You Have a New (BuddyPress) Message vs Toast Popup Notification News Alert