Yes, SO has flagging for notifying the moderators about a post (usually spam), and closing for off-topic or duplicates.
I was thinking of just keeping the "flag" button as it is now, but allow possible reasons*. If a question gets N flags it could get closed or hidden, depending on the reason (e.g. spam would get hidden, off-topic would be closed, duplicates would be redirected).
*BTW, is it possible to customize a list of reasons for closing?