|Client versions of Windows have supported multiple user accounts and users for a long time, but only one at a time. However many input devices you might manage to configure, however many monitors, desktops, applications, etc, there can be only one active window at any given time. All user interaction is with that one window. This is a basic concept in Windows. No special hardware, configuration, or third party software can change this.|
Server versions of Windows allow one locally logged in user plus a number of others logged in via terminal services. No client version of Windows has ever supported this. But even then there can be only one locally logged in user active at any given time.