From the rules:
“Quad RPG” means “Quick and Dirty Role-playing Game.” This simple RPG is designed to be picked up and played with not even a moment’s notice and only a modicum of necessary rules-checking. All you need is a mechanism for generating a set of random numbers (dice and cards are common), maybe a handful of pennies or just a notepad to mark some tallies, and this document (and hopefully if I’ve done my job well enough, you won’t even need that after a good read-through). Pen and paper can also be quite useful.
That’s really all there is to it. Quad is a simple RPG initially designed to fit on the front and back of a single sheet of paper. It’s meant to be picked up and played immediately, and serve as a nearly-invisible foundation for games of just about any theme and genre. It was initially released to the crowds at Dragoncon 2008, and is also now available as a free github download (most recent version is 1.2.1 is a new document conversion and cleanup from May 2016).