This program merges the capabilities of x2x and vncviewer. It will allow
a machine with an X display and a machine with a VNC server running on its
main screen to act as if they were two displays connected to one machine.
When you move your mouse pointer off the screen in a direction of your
choosing, the pointer will appear on the other screen instead.

WWW: http://fredrik.hubbe.net/x2vnc.html