What follows are command specifically pertaining to X11.
You can invoke the X server with
$ X -quiet -query remotemachineaddress
to get a graphical login screen for the remote machine. See xdm.
xbiff displays a small box indicating whether your local Unix inbox has mail. Start with:
xcalc draws a window with a scientific calculator. The easiest way to operate the calculator is to click the buttons. The calculator understands order of operations (multiply before add) and provides common functions such as sine, square root, and the values of e and pi. The calculator normally displays eight digits and supports scientific notation.
An X display manager used to manage graphical sessions of multiple users. It is usually started automatically as a system service to present the user with a GUI login screen instead of the console login prompt. Modern systems usually use GDM (the GNOME Display Manager) and KDM (the KDE Display Manager) instead.
A normal program not a part of X11 itself, for viewing DVI form