xdmx 6.8.2-10.4 (i386 binary) in ubuntu hoary

 Xdmx is a proxy X server that uses one or more other X servers as its display
 devices. It provides multi-head X functionality for displays that might be
 located on different machines. Xdmx functions as a front-end X server that acts
 as a proxy to a set of back-end X servers. All of the visible rendering is passed
 to the back-end X servers. Clients connect to the Xdmx front-end, and everything
 appears as it would in a regular multi-head configuration. If Xinerama is enabled
 (e.g., with +xinerama on the command line), the clients see a single large screen.