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.
Comments about Xpra as an Alternative to Xephyr


- Xpra is Free and Open Source


Xephyr allows a second x11 session to be run within a window locally. Xpra is for remote sessions.