It's a generic game system, but at the time (1997 or so) it was the only game system I had seen with character creation governed only by the cooperation of the Storyteller (GM) and the other players.
Players were actively encouraged to define their player using only words, then work with the Storyteller to assign traits to those words. This meant I didn't have to level up several times to play a seasoned veteran of war or a world renown professor of archaeology. And I didn't have to worry about bookkeeping like I did in point-buy games.
The Window was also my first brush with a "step-die" system of any kind. System-wise it has a lot in common with
Tales From the Floating Vagabond (it even uses a d30). It plays very fast and loose, much moreso than other step-die systems that I've had experience with (including
Savage Worlds).
Back in the late 1990s, this (fast play) was a huge thing for me as I was drowning in
AD&D,
Shadowrun, and
Rifts, respectively (all of which were chock full of rules, rules, and more rules). I guess, The Window was the first truly complete "rules light" game system I stumbled across.
Attached is a copy of the most recent revision. Just ignore the godawful intro. I pushed really hard to have that removed this time around (and the original author has since said that he dislikes it nearly as much as I do), but fandom won out. Damn fandom.
There are some interesting (albeit poorly translated) notes on
Shadowrun conversion
here, which is what initially piqued my interest in the system.