A method in a computer system for displaying data generated by a shared application on a host computer system on both a host display of the host computer system and a shadow display of a shadow computer systems The host computer system has a window manager for managing windows displayed on the host display. The shadow computer system has a window manager for managing windows displayed on the shadow display. Under control of the host computer system, a Share System executes the shared application. Then, the Share System registers a host window with the windowing system of the host computer system. Upon registration of the host window, the Share System sends a notification of registration of the host window to the shadow computer system. At the shadow computer system, the Share System receives the sent notification of registration of the host window. Upon receiving the sent notification of registration of the host window, the Share System registers a shadow window with the windowing system of the shadow computer system so that the window wing system of the shadow computer system can send messages to the shadow window and receive data to display in the shadow window.