A role-playing game system, is a set of game mechanics rules used in a tabletop role-playing game (TTRPG) to determine the outcome of a character's in-game actions.
The staff of Chaosium realized by the late 1970s that the RuneQuest system designed by Steve Perrin had enough potential to become the "house system" for the company, which could then use one set of game mechanics for multiple games; Greg Stafford and Lynn Willis proved this correct by slimming the RuneQuest rules down into the 16-page Basic Role-Playing (1980).[1] Hero Games used the rules for their Champions game to form the basis for their Hero System.[1] The house system from Pacesetter Ltd focused on a universal "action table" consisting of one chart to be used for resolution of all actions within the game.[1] Steve Jackson wanted to design a role-playing game rules system and had three goals in mind: this system must be detailed and realistic; it must be logical and well-organized; and this system must be adaptable enough to be used with any setting and level of play; this system of rules was eventually released as GURPS (1986).[1] The Palladium house system was initially derived from Dungeons & Dragons and was ultimately used in all of the Palladium Books titles.[1] Mekton II (1987) by R. Talsorian Games debuted the full version of their Interlock System of rules.[1]
Game Designers' Workshop released the second edition game rule system in 1990, and decided to use its game system as their house system, under which they would design all of their subsequent role-playing games.[1] Amazing Engine from TSR was a universal game system, intended as a simple system for beginners.[1] Hero Games partnered with R. Talsorian in 1996 and worked together to create a simpler rules system to draw new players, by merging the Hero System with the Interlock system and calling it Fuzion.[1] (1996) was built on the SAGA storytelling game system from TSR, which used a resource management system involving cards instead of die rolls.[1] TSR published the Alternity (1997) universal game system, which was intended only for science-fiction games.[1] The Masterbook system had failed to catch on as a house system for West End Games, so they published the D6 System which was based on their successful .[1]
While early role-playing games relied heavily on either group consensus or the judgement of a single player (the "Dungeon Master" or Game Master) or on randomizers such as dice, later generations of narrativist games allow role-playing to influence the creative input and output of the players, so both acting out roles and employing rules take part in shaping the outcome of the game.
An RPG system also affects the game environment, which can take any of several forms. Generic role-playing game systems, such as Basic Role-Playing, GURPS, and Fate, are not tied to a specific storytelling genre or campaign setting and can be used as a framework to play many different types of RPG. Others, such as Dungeons & Dragons, are designed to depict a specific genre or style of play, and still others, such as Paranoia, are not only genre-specific but come bundled with a specific campaign setting to which the game mechanics are inseparably tied. In fact, in more psychological games such as Call of Cthulhu, King Arthur Pendragon, Unknown Armies, and Don't Rest Your Head, aspects of the game system are designed to reinforce psychological or emotional dynamics that evoke a game world's specific atmosphere.
Many role-playing game systems involve the generation of random numbers by which success or failure of an action is determined. This can be done using dice (probably the most common method) or cards (as in Castle Falkenstein), but other methods may be used depending on the system. The random result is added to an attribute which is then compared to a difficulty rating, although many variations on this game mechanic exist among systems. Some (such as the Storyteller/Storytelling System and the One-Roll Engine) use dice pools instead of individual dice to generate a series of random numbers, some of which may be discarded or used to determine the magnitude of the result. However, some games (such as the Amber Diceless Roleplaying Game and Nobilis) use no random factor at all. These instead use direct comparison of character ability scores to difficulty values, often supplemented with points from a finite but renewable pool. These "resource points" represent a character's additional effort or luck, and can be used strategically by the player to influence the success of an action.