ModemLockDown

Controlling each PC it is installed on, ModemLockDown either allows internet access or it doesn't. With either the click of a button or use of the time limit controls, as the supervisor, you're in control of when the internet can be accessed and when it can't. And with ModemLockDown's built in support for OpenDNS and their FamilyShield service, you have set and forget access to additional security and adult content filtering. Low cost, lifetime license, free upgrades, no on-going fees or subscriptions, volume discounts and a free 30 day trial.

Limitations:

30-day trial