xdm - 1:1.1.11-6.1 main

xdm manages a collection of X servers, which may be on the local host or
remote machines. It provides services similar to those provided by init,
getty, and login on character-based terminals: prompting for login name and
password, authenticating the user, and running a session. xdm supports XDMCP
(X Display Manager Control Protocol) and can also be used to run a chooser
process which presents the user with a menu of possible hosts that offer
XDMCP display management.