Jamie Zawinski noted the 30th anniversary of XScreenSaver’s version 1.0 release with the original USENET post and more bits of fun trivia although he notes that version 1.0 of XScreenSaver is missing. XScreenSaver must be one of the longest continually updated software projects out there, it has great stuff from the past like your flying toasters and almost everything else including more modern screen savers that reference things like one of our current pandemics.
The main competitor to XScreenSaver in the screen saving space was After Dark by Berkeley Systems but that was a commercial software package for Macs and Windows computers hasn’t been updated since 1996 although you can emulate old versions and I was surprised to find out you can buy modern macOS versions of three of the After Dark screen savers. Even more surprising is that if the Wikipedia page for After Dark is to be believed, Microsoft may own the rights to After Dark after Activision is acquired.
XScreenSaver is a free download for macOS, X11-based Linux systems, iOS, and Android. XScreenSaver is unavailable for Windows.