x2vnc (win2vnc)
This program will let you use two screens on two different computers as if they were connected to the same computer. The program will open a small (one pixel wide) window on the edge of your screen. Moving the pointer into this window will trigger the program to take over your mouse and send mouse movements and keystrokes though the RFB protocol to a VNC server running on another machine. When the pointer is moved back towards the opposite edge on the other screen, the mouse is then released again.
