XScreenSaver is a modular screen saver and locker for the X Window System. This is a highly customizable software that allows using any program that can draw on the root window as a display mode. More than 190 display modes are included in this package.

Before running a graphic demo chosen at random, the XScreenSaver program waits until the keyboard and mouse have been idle for a period. The program turns off as soon as there is any mouse or keyboard activity. It can also lock the screen, either immediately or after a longer idle period according to the users’ specifications.

XScreensaver contains two parts: the XScreensaver itself, known as driver or daemon, which detects idleness and does locking; and the large number of graphics demos launched by the software.

Any X program that is drawn on the root window can be used with XScreensaver, regardless of the programming language or structure, or the libraries used by them. The XScreensaver daemon detects when the user is idle, locks, and checks passwords and all the other book-keeping. All that the program need to do is draw.
XScreensaver works better than xlock and xautolock programs because new graphics hacks can be installed with Xscreensaver without requiring to recompile or rerun.
XScreenSaver works on any computer with the X Window System including all Unix systems (Linux, BSD, etc.); and VMS. It also works well on MacOS X systems