xnest 2:1.19.6-1ubuntu1 (amd64 binary) in ubuntu bionic

 Xnest is a nested X server that simply relays all its requests to another
 X server, where it runs as a client. This means that it appears as another
 window in your current X session. Xnest relies upon its parent X server
 for font services.
 .
 Use of the Xephyr X server instead of Xnest is recommended.
 .
 More information about X.Org can be found at:
 <URL:https://www.x.org>
 .
 This package is built from the X.org xserver module.