XScreenSaver is the standard screen saver collection shipped on most Linux and Unix systems running the X11 Window System. I released the first version in 1992. In 2006, I ported it to MacOS X 10.4.
On X11 systems, XScreenSaver is two things: it is both a large collection of screen savers; and it is also the framework for blanking and locking the screen.
On MacOS systems, these screen savers work with the usual MacOS screen saving framework (X11 is not required).
These details are provided for information only. No information here is legal advice and should not be used as such.