Back in 2013, Eurogamer published a look at what Ion Storm Austin's seminal game Deus Ex could have been, replete with excerpts of an original design document annotated by game director Warren Spector.
Now, it appears a Reddit user convinced the writer of that article and convinced him to share his full copy of the document, along with copies of Ion Storm design documents (circa 2004) for a Thief 4 game that never happened and a packet that includes design documents for a third Ion Storm Deus Ex game (along with a seemingly random assortment of other documents, including what appears to be notes given by film producer Laura Ziskin to Warren Spector on the draft of a script for a Deus Ex movie.)
All of these documents make for fascinating reading, and the Deus Ex design doc is especially notable for game devs because it reveals how significantly the game evolved over the course of its development.
For example, a cursory skim of the document (republished below) reveals that the Deus Ex team originally hoped to ship the game (then referred to as Shooter: Majestic Revelations) by 1998 (it shipped in 2000) with a third act that took place on a space station (cut from the final game) and, if they could swing it, maybe some kind of cooperative multiplayer mode (they couldn't.)
While most of what you'll find in this document has already been discussed at length by the Deus Ex team -- see Warren Spector's original postmortem of the game and, more recently, our oral history of Deus Ex's development -- it's still intriguing to page through a written record of what the game which has influenced so many game designers could have been.