id Software for the same reason everybody else says id Software. Also, the lavafall texture is from GothicDM (I think) so credit there as well
Base:
d at a strategic and well-defended outpost on the edge of what was only weeks ago a valley of rubble but what is now a thriving demon city. The UAC had erected the compound fast, but unfortunately the demons were faster, and after valiant but hopeless resistance the monsters had overrun the base. You are now the only living human in the entire compound, and probably in all of Hell. With the researchers dead, your comrades twisted into mindless monsters and UAC's plan generally in the toilet, there is only one thing you can do: get out of the base and find a way back to Earth alive. Your chances of making it out are slim, but then again you wouldn't be the first person to escape from Hell. With this in mind, you set out, with nothing but your pea shooter, a few dozen rounds of ammo and your iron will to live...