The Doom Bible

I just love this: here's the Doom Bible, written by Tom Hall, the original design manual for the (at the time of writing still unfinished) video game Doom. It outlines ideas for Doom, including an intricate plot, most of which were later scrapped in favor of a more simple, straightforward game. So whole passages regarding the back story are totally different to the final release. Also, there are multiple characters mentioned, whereas in the final game, you only had the opportunity to play as an anonymous "Space Marine". This change in direction was what ultimately led to the resigning of Tom Hall, the original creative director of the game.

Parts of the manual are more like a collection of notes or brain-storming, with passages going like "Insert interesting description of behavior and how they are beat here."

You can also find out that the BFG 9000 has been in the game all along:

BFG 2704 (red). Horrible hallway-scouring weapon. Damages user a bit. Awful recoil. BFG stands for "Big Fucking Gun." Safest use: back to wall, distant target.

Also, apparently one of the first things Hall planned was a "nude" mode, check out these command-line parameters:

DOOM /bubbies Replace all actors with naked women
DOOM /prude Cancels effects of bubbies parameters
DOOM /drunk Occasionally invokes the bubbies mode

The Doom Bible is dated November 28, 1992 and is a lot of fun to read. You just gotta love the whacky typeface, sketchy in-joke descriptions and general nerdiness attached in this, thankfully preserved, document.

Doom World: The Doom Bible