Despite Odamex, we have Prboom[1], PrBoom+[2] ("prboom-plus" package) and
Doomsday Engine[3] as alternatives to the Doom source port.
Zandronum is proprietary/non-free software because it doesn't make any effort
to remove the proprietary/non-free functional data from the parent project:
ZDoom (be the functional data: software, scripts, documentation, fonts and so
on) [4].
There is a project which does make such effort to remove the
proprietary/non-free functional data, and which is also based on ZDoom:
GLOOME[4]. Based on this proofs, I (and many others here as well) find GLOOME
to also be free software, despite the fact that no one has yet sent GLOOME
for review and approval at the Free Software Directory[5].
Also for a game to be played in this source ports, I recommend Freedoom 1 and
2, and FreeDM if you want some deathmatch. FreeDM is part of the Freedoom
project.
REFERENCES
[1] https://directory.fsf.org/wiki/PrBoom
[2] https://directory.fsf.org/wiki/PrBoom%2B
[3] https://directory.fsf.org/wiki/Doomsday_Engine
[4] https://trisquel.info/en/forum/doomdoom-ii-trisquel#comment-76944
[5] https://directory.fsf.org/wiki?search=GLOOME&title=Special%3ASearch
[6] https://directory.fsf.org/wiki/Freedoom
