Does anyone know of a computer turn-off program?

Has anyone heard of a program that you can set for a certain time, that will turn off (or make inaccessible except by an administrator) a computer? Like for instance, if someone's got a roommate and only wants them on for 10 minutes, and sets the timer, and at the end of 10 mins, the roommate is forced to get off the computer because it restarts or whatever? If so, what is the name of the program, how much does it cost and where can it be found?