The Cortex System is a generic RPG system based on the Sovereign Stone System, and was developed by Margaret Weis Productions, Ltd for the Serenity (role-playing game). It was subsequently used for their licensed Battlestar Galactica and Supernatural RPGs, and brought out as a stand-alone system in the Cortex System Role Playing Game book (also called the Cortex Classic System Role Playing Game). Serenity, using the Cortex System, was the 2005 Origins Award Gamer's Choice Role Playing Game of the Year.
Note that despite the similar name, the Cortex System is not the Cortex Plus system, also produced by Margaret Weis Productions.
The basic system
The system uses dice with 2, 4, 6, 8, 10, and 12 sides, described with the standard role-playing game notation of d2, d4, d6, d8, and so on, and the basic resolution system involves adding up the total on all your relevant dice and comparing it to a static target number. The three parts of your dice pool are your relevant Attributes (Agility, Strength, Vitality, Alertness, Intelligence, and Willpower) which range from d4 to d12+d4, your relevant Skill (from a list of 22) which range from 0 to d12, and any relevant Assets (positive character traits) or Complications (negative traits). Situational advantages can be represented either by changing the target difficulty number or increasing or reducing the number of faces on the dice rolled.
The Cortex System also uses Plot Points, which increase characters' survivability and give players greater control over events in the game. Players can spend Plot Points to gain extra dice when making a die roll, reduce the damage from an attack, or even make changes to the storyline. Some Assets also require the expenditure of Plot Points. At the end of a game session, excess Plot Points are converted to Advancement Points, which a player spends to improve his or her character's abilities.
The game uses a point-buy system with a default initial spread between attributes, skills, and traits (the collective name for advantages and complications) based on the intended power level of the game. This is similar to the silo'd point buy and special abilities and character flaws used in a variety of other role-playing games, such as Merits and Flaws in White Wolf Publishing's original World of Darkness, Qualities and Drawbacks in Eden Unisystem, and Edges and Hindrances in Pinnacle Entertainment's Deadlands and Savage Worlds games (to which the Serenity system bears a strong resemblance).
Published games using the Cortex System
- Serenity (role-playing game) 
- Battlestar Galactica Role Playing Game 
- Demon Hunters Role Playing Game 
- Cortex System Role Playing Game 
- Supernatural Role Playing Game
- "D6G Episode 18: Serenity RPG reviewed & interview with designer". The D6 Generation. October 30, 2008. Retrieved March 31, 2013.
- RPG.net review of Cortex Classic
- Cortex Classic System RPG listing
- RPG Geek Serenity RPG page
- Chambers, Jamie (2005), Serenity Role Playing Game, Margaret Weis Productions
- Chambers, Jamie (2007), Battlestar Galactica Role Playing Game, Margaret Weis Productions, ISBN 9781931567558
- Chambers, Jamie (2008), Demon Hunters Role Playing Game, Margaret Weis Productions, ISBN 9781931567473
- Chambers, Jamie (2008), Cortex System Role Playing Game, Margaret Weis Productions, ISBN 9781931567794
- Chambers, Jamie (2009), Supernatural Role Playing Game, Margaret Weis Productions, ISBN 9781931567497