Terminal Services Manager can restart or power off a monitored server. Both actions ask for a simple confirmation first, then run against every selected server.
Select one or more servers on the Servers tab, then:
A confirmation dialog appears for the action you picked.


Click Restart or Power off to go ahead, or Cancel to abort. When more than one server is selected, the prompt says how many. The request is then queued and carried out on each server; watch the Application log for the result.
There is no message field on these prompts. If you want to warn users before the action, send a message first with Sending a message or a message preset.
To log a user off rather than restart the whole server, use the per-session Log off action on the User sessions tab instead.