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.

Features

• Block Sharing Login Info
• Flexible Settings
• Timed Lockouts
• Lockout & Logout Feature
• Record Login IP
• Display Access Logs

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.