Trisquel has a free culture standard, too, and AssaultCube doesn't fit that
standard. Many of the art assets are under proprietary licenses. It doesn't
really matter; the AssaultCube in Ubuntu's repos is years out-of-date, so you
aren't able to connect with many people.
I don't know about Sauerbraten.
Also note that Ubuntu has multiple repositories, and Trisquel only pulls from
the main one (I think Universe is the one Trisquel pulls from and the other
one is called Contrib or something, but I'm not sure; not familiar with
Ubuntu's repos).
