Charles Fulton

This plugin suppresses features of the Multisite site creation process:
<ul>
<li>It suppresses the welcome email sent to new site administrators on site creation</li>
<li>It cancels the site creation process if the given email does not exist, instead of creating a local user</li>
</ul>
It also flushes rewrite rules on site creation to address https://core.trac.wordpress.org/ticket/20171.
<h3>Privacy</h3>
This plugin neither collects nor stores any personal, private, or identifying information about any user.

Site Creation Utilities

This plugin improves the Multisite site creation process by eliminating undesired features.

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.

Site Creation Utilities vs Network Username Restrictions Override