1. Automatic screensaver for X The purpose of xscreensaver is to display pretty pictures on your screen when it is not in use, in keeping with the philosophy that unattended monitors should always be doing something interesting, just like they do in the movies. The benefit that this program has over the combination of the xlock and xautolock programs is the ease with which new graphics hacks can be installed: you don't need to recompile this program to add a new display mode, you just change some resource settings. Any program which can be invoked in such a way that it draws on the root window of the screen can now be used as a screensaver without modification. The programs that are being run as screensavers don't need to have any special knowledge about what it means to be a screensaver. From Debian 3.0r0 APT

2. The xscreensaver package contains a variety of screensavers for your mind-numbing, ambition-eroding, time-wasting, hypnotized viewing pleasure.Install the xscreensaver package if you need screensavers for use with the X Window System. From Mandrake 9.0 RPM

3. graphics hack and screen locker, launched when the user is idle From whatis