Source code is also available. To compile for MacOS or iOS, you need XCode.
iPhone and iPad users:
(Note that most distros divide xscreensaver into three or more binary packages. Look for packages whose names begin with "xscreensaver" and end with a random assortment of the words "data", "extra", "extras", and/or "gl".)
I distribute only source code for X11 systems. However, I strongly recommend that you install a binary package rather than compiling it yourself. There are many build dependencies.
There is no Windows version of xscreensaver, and there never will be. Please stop asking. Microsoft killed my company, and I hold a personal grudge. I don't use any Microsoft products and neither should you.