xscreensaver may have non-free licenses in parts of it.

The file breakout.asm in xscreensaver shows

; Brick Out by Blake Ramsdell <name at domain> http://www.blakeramsdell.com

; A poor attempt at brick out with no player involved. Maybe someday I'll
; let you play it, or you can view this as an exercise for the reader to put
; in a paddle that is user-controlled.

; I guess this is Copyright (C) 2007 Blake Ramsdell, and you have a license to
; do whatever you want with it, just tell me what you did and give me a
; mention. If you want to sell it, and you make a billion dollars, then good
; for you. You might at least throw a party and invite me.

; The gist of it is pretty simple -- you have a ball, and the ball has an X
; and a Y velocity. When it hits something, it bounces off of it. If the thing
; that it hits is not a wall, then it erases it. Pretty dead-simple behavior.

; I don't like the vertical movement -- there's a shortcut in here somewhere
; to make it less computationally expensive I think. Right now it just does a
; two byte add and subtract of $20.

; The ball motion is also a bit weird looking. I don't know if this is an
; artifact of the simulation environment combined with a normal tearing
; artifact related to refresh or what.

; Blake Ramsdell, May 2007

So even though do whatever you want with it may be nice the just tell me what you did may make this non-free software as

https://www.gnu.org/licenses/license-list.html

shows non-free licenses like Reciprocal Public License (#RPL)

The Reciprocal Public License is a nonfree license because of three problems. 1. It puts limits on prices charged for an initial copy. 2. It requires notification of the original developer for publication of a modified version. 3. It requires publication of any modified version that an organization uses, even privately.

and

Sybase Open Watcom Public License version 1.0 (#Watcom)

This is not a free software license. It requires you to publish the source code publicly whenever you “Deploy” the covered software, and “Deploy” is defined to include many kinds of private use.

and

Old Plan 9 license (#Plan9)

This is not a free software license; it lacks essential freedoms such as the right to make and use private changes. Of course you should not use this license, and we urge you to avoid any software that has been released under it.

And this license (the one breakout.asm is licensed under) also shows modification or even use requires telling Blake Ramsdell about any use/"what you did", even if done privately.

So like the other non-free licenses this program may be non-free because of the license.

There is also a pacman screen saver in it, and wikipedia shows at

https://en.wikipedia.org/wiki/List_of_Pac-Man_clones

Mighty Mouth is a game by A-1 Machines that District Court Judge Warren Keith Urbom described as "for all practical purposes, identical to ...Pac-Man"[3] Among the similarities cited were the color and shape of the player character and ghosts, the maze configurations, the sound effects, the paths of the characters in the attract mode and the paths of the characters in both the attract mode and a game where the player does not move.[4] Midway, owners of the Pac-Man copyrights, were granted summary judgment for copyright and trademark infringement in 1983.[5]

So I do not know if the Pacman screensaver can be distributed at all.

I do not yet know if more non-free software like breakout.asm or non-free artwork (as in not even shareable/copyrighted and not to even be distributed by 3rd parties, like Gnu/Linux distros) is in or distributed with xscreensaver or any extra xscreensaver part.

I think these may be easy to remove if needed though.