SIMPLE Fallout is a tabletop roleplaying game set in the Fallout universe, with mechanics inspired by the Fallout games. It is used in J.E. Sawyer's Fallout Role-Playing Game.
While Fallout proper and many other Fallout TTRPGs have used a percentile die system, SIMPLE uses a 3d6 system. It is designed to be faster to play than other alternatives while still maintaining a high degree of tactical depth. It is currently untested and under continuous development. Simple is the game system used to run Fallout tabletop games. The system used in the Fallout computer games was SPECIAL. SPECIAL was a variant of Steve Jackson Games' GURPS.
Whoa, whoa, whoa! What's up with all of these acronyms?
GURPS = Generic Universal Role Playing System. GURPS was designed to be an extremely flexible, extensible game system. Using GURPS, players can run fantasy games, sci-fi games, or even cowboy-western style games. SPECIAL = Strength, Perception, Endurance, Charisma, Intelligence, Agility, Luck. SPECIAL was designed to work for Fallout's computer medium. Though it used a lot of different formulae to derive attributes and calculate the results of combat checks, it was not problematic because human beings were not required to do the calculations.
Okay, so what's up with Simple?
Simple is designed to be easy to get into, but have long term flexibility for players. It is not intended to be as flexible as GURPS or as detailed as D&D 3.5. Though the mechanics for high technology and high skills can become more complex, the basics are, well, simple.
These rules assume that people want to play Fallout tabletop games because they enjoy the setting and are more interested in the idea of what their characters can do in the game world than what they can do on a piece of paper. You will not find rules on aging penalties, rolling for weather, or how to create bigger and badder versions of equipment. It uses levels and hit points for ease, but does not use things like alignment or class.
The Simple rule system requires the use of three types of dice: six-sided (d6), eight-sided (d8) and ten-sided (d10). These dice are mostly used to calculate weapon damage. Skill checks make frequent use of two ten-sided dice, which are sometimes referred to as "percentile" with one die representing the tens digit and the other die representing the singles digit (d100).
Characters are statistically defined through Primary Attributes, Derived Attributes, Floating Attributes, Skills, Perks, and Traits.