Magic Kicker - 3 User License
Prevent Multiple People Logging Into a Single Account
3 User License, suitable for install on 3 copies of Wordpress 3.0 or higher. If you want to install on more than 3 Wordpress please consider the Unlimited License.
3 User License is for 3 hosts (three domains or sub domains)
Magick Kicker is a stand alone plugin which you can use on any Wordpress site.