Freedoom: Phase 1 is a Doom styled first person shooter game using the
Doom engine, featuring Four chapters, nine levels each, totalling 36
levels.
There is a massive back catalog, spanning over two decades, containing
thousands of Doom levels and other modifications (“mods”) made by fans
of the original Doom game. Freedoom aims to be compatible with these and
allows most to be played without the original Doom datafiles.
Freedoom: Phase 1 aims for compatibility with The Ultimate Doom,
also known as plain Doom or Doom 1.