mogita

NOTE: ONLY works with multisite (aka WordPress Network) mode for now.
A super-easy-to-use Multisite WordPress news broadcasting tool for the Super Admin of the Network.
This plugin can be helpful for the Super Admins to push a notification, some kind of messages, even some Ads if they like, to every site admins who registered under your Multisite WordPress network. The added widget will go to the first place of all widgets, unless the site admins move it elsewhere.
This is a very simple task but yet no plugins ever met my simple need, so I made one for myself, and hope it helps you too.
Key Features:
<ul>
<li>Add a widget to every site admin’s dashboard (by Super Admin only)</li>
<li>Support HTML content</li>
<li>Comes at the top of all widgets</li>
<li>Site admins can move or hide it as they wish</li>
<li>Multi languages support (available in English and Chinese till now)</li>
</ul>
You can find the configuration page at Manage Network -> Settings -> Dashbaord Broadcast.

Multisite Dashboard Broadcast

Place a widget on top of every site's dashboard under the same Multisite installation, containing whatever content the Super Admin writes.

Emanuela Castorina

This plugin in a multisite installation shows the ID of the current site/blog in the admin bar menu. The ID of the current site/blog is linked to the site info page. 
It adds also a custom column with site id information inside the sites list table. 
It can be installed only on a multisite.

Wp Show Site ID

This plugin in a multisite installation shows the ID of the current site/blog.

Multisite Dashboard Broadcast vs Wp Show Site ID