Thanks for the answer.
Red Eclipse isn't Free Software.
Debian have put it in "contrib" repositories and data in "non-free"
repositories ( you can check this
http://packages.debian.org/search?searchon=names&keywords=redeclipse ).
I see also Tremulous
http://packages.debian.org/search?suite=default§ion=all&arch=any&searchon=names&keywords=tremulous
in the same situation but package is present in Parabola GNU/Linux
repositories https://parabolagnulinux.org/packages/?q=tremulous (this
confuses me).
I see that the major problem for most of open source games are the data files
(artwork,sound...) that are released under Free Software non-compatible
licenses and not the code.
