Xnee receives X11 protocol data (e.g. XEvents) from an X server and
prints them to a file (or stdout).  By recording events such as
MapNotify, the replaying of events can be synchronized.  This is not only
useful but essential.  We cannot replay or regenerate keyboard-events to
a window before it's ready to "receive" events.  By recording events and
requests synchronization can be implemented.  Xnee can also distribute
events (both when recording and replaying) to other displays.

WWW: http://www.sandklef.com/xnee/