Skulltag for Linux brings classic Doom into the 21st century, maintaining the essence of what has made Doom great for so many years and, at the same time, adding new features to modernize it, creating a fresh, fun new experience.
For help, see the Setup guide. You need a copy of Doom (or Heretic, Hexen, or Strife) to play Skulltag. If you don't have one, Steam sells it cheapest for $10 or GOG. Once you download it, Skulltag takes care of the rest.