Who has ever been working on more than one Linux computer simultaneously knows the problem: I need this window on the other computer's screen.

The solution: xmove. Usage is quite simple: start another XServer on port :1 by issueing the command

xmove -port 1

All windows that shall be movable to other displays should use this server. By default xmove displays them on the active XServer. To move them to another display type

xmovectrl :1 -moveall :10

where :10 denotes the 10th XServer. Because the standard X protocol is used, this also works over ssh or together with Xnest.