x11-common 7.0.0-0ubuntu40 (amd64 binary) in ubuntu dapper

 x11-common contains the filesystem infrastructure required for further
 installation of the X Window System in any configuration; it does not
 provide a full installation of clients, servers, libraries, and utilities
 required to run the X Window System.
 .
 A number of terms are used to refer to the X Window System, including "X", "X
 Version 11", "X11", "X11R6", and "X11R7". The version of X used in Debian and
 Ubuntu is derived from the version released by the X.Org Foundation, and is
 thus often also referred to as "X.Org". All of the preceding quoted terms are
 functionally interchangeable in an Ubuntu system.