Xpra: (GNU) screen for X applications (partiwm.org)

Xpra is 'screen for X' -- it allows you to run X programs, usually on a remote host, direct their display to your local machine, and then to disconnect from these programs and reconnect from the same or another machine, without losing any state. (see the FAQ: http://partiwm.org/browser/README.xpra also, for more)