Walid Sadfi

The Conditionnal Maintenance Mode for WordPress plugin allows the administrator to enable or disable maintenance mode for selected user roles. The administrator can also customize the maintenance message that will be displayed to users who do not have the necessary roles.
This plugin is useful when you are performing updates or maintenance on your website and want to limit access to certain users while you work.

Conditionnal Maintenance Mode for WordPress

This plugin allows the administrator to enable or disable maintenance mode for selected user roles and customize the maintenance message.

ymjid

Webinfos allows to admins to show a customisable message in the dashboard in is own dashboard widget. 
The plugin supports several custom messages (only one will be visible on the dashboard). The plugin is translatable but only French is supported for now. 
Webinfos integrate a feedback form to report a bug and/or give suggestions to the plugin author.
With Webinfos you can :
<ul>
<li>Add Contact informations (photo, phone number, email) and choose if you show them or not.</li>
<li>Upload logo, video or just files as attachments.</li>
<li>Use HTML tags in the message.</li>
</ul>

Webinfos

Webinfos allows to admins to show a customisable message in the dashboard.

Conditionnal Maintenance Mode for WordPress vs Webinfos