Roy Tanck

This plugin will help you:
<ol>
<li>Find plugins and themes that are not active on any blog.</li>
<li>Determine the impact in case a theme/plugin needs to be upgraded, removed or reconfigured.</li>
<li>See if a widget is in use on any blogs, and track down where.</li>
<li>Find users who do not have a role on any site (and are not network administrators).</li>
</ol>
This plugin currently does nothing on single-site WordPress installs.

Network Admin Assistant

Helps you manage a WordPress network by displaying useful statistics.

Daniel Westermann-Clark

By default, WordPress network usernames cannot contain anything but lowercase letters and numbers. This plugin adds network options to let you include hyphens, underscores, or uppercase letters, if desired.
Furthermore, this plugin gives you the option to allow email addresses as usernames, or to allow all-numeric usernames (e.g. “1234”).
Finally, this plugin lets you override the minimum length for usernames (which defaults to four characters).
To follow updates to this plugin, visit:
https://danieltwc.com/
For help with this version, visit:
https://danieltwc.com/2011/network-username-restrictions-override-1-0/

Network Username Restrictions Override

Does what it says!

Override restrictions on WordPress network usernames.

Network Admin Assistant vs Network Username Restrictions Override