Windows 7 has this ability built-in. You can use a GUI or command line version of the 'shutdown' command, but you need to set up all the PCs that you want to be able to control first:
1. Enable the 'Remote Registry' function on each remote PC to Automatic:
a. Go to Start, and in the search bar type services.msc
b. Scroll down the list of services to Remote Registry
c. Right-click it and select Properties
d. Change the 'Startup type' to Automatic
e. Click OK
2. Allow 'Windows Management Instrumentation (WMI)' through Windows Firewall:
a. Go to Start, type 'allow a program', and select Allow a program through Windows Firewall
b. Scroll down to Windows Management Instrumentation (WMI) and tick the Home/Work tick box
c. Click OK
3. (Optional) If you are not on a domain, then you need to create an administrator account on each PC with the same username and password which you will use to log in to your PC; this gives you administrative access. If you are on a domain, you can just log in as domain administrator on your PC and that will work without the need of additional user accounts.
Once the above is done, you can go to Start and type:
shutdown /i
to start the interactive GUI. From there, either Browse for PCs or manually Add them by name. Select a PC, a reason, and do it.
To do the same from a command line (for use in a script or similar), the shutdown command can be used on the command line with other switches.
For instance, to perform a basic shutdown by PC name or its IP address:
shutdown /m \\pc-name /s
shutdown /m ip-address /s
To see all the other command line options, type:
shutdown /?
Please consider that users might lose unsaved information etc., especially if you disable the warning message and use the force option.
ETA: I got beaten to it by UsernameIssues... must learn to type more quickly.
