The application is called PsShutdown, and is downloadable for free:
http://technet.microsoft.com/en-us/sysinternals/
PsShutdown is quite similar to “regular” shutdown – the former accepts the same parameters as the latter, but has various additional features, such as logging off users, locking the work station, and foremost: shutdown of the system when nobody’s logged in, or when the console is locked.
Usage sample
Suppose you need to reboot your system once a week. You would then create a Scheduled task (using the built-in Windows task scheduler), set to be executed once a week, using a privileged account (i.e. an account which is capable of doing the system reboot), and run this command:
psshutdown -f -r -m “automated planned reboot” -e p:0:0