Binary package “xserver-xephyr” in ubuntu precise

nested X server

 Xephyr is an X server that can be run inside another X server,
 much like Xnest. It is based on the kdrive X server, and as a
 result it supports newer extensions than Xnest, including render and
 composite.
 .
 More information about X.Org can be found at:
 <URL:http://www.X.org>
 .
 This package is built from the X.org xserver module.