CLI

How to: do a quick check on who is connected to the server via RDP

Apart from obvious ways to do it via Windows Server GUI which is the long way (plus if you working with multiple versions like Server 2003 and 2008 it differs slightly and requires you to remember the “path” through GUI to find this information) there are CLI tool to accomplish this: qwinsta available starting from Windows XP, if How to: do a quick check on who is connected to the server via RDP