A set of rules used by a game development company for almost every game they publish. It is much cheaper to create the system once, and then tweak it for a specific game, than to develop a unique system for each game. It also helps with sales because players will already know the basics, and won't have to learn a whole new set of rules. If your system requires something unusual, such as particular dice or tokens, they can generally be reused between games. However, using a House System can backfire if the system doesn't fit the genre it's being applied to.
Distinct from a Universal System in that, while a House System may be used for multiple genres, it is not released as an independent cross-genre product and is only used by one company. However, many (even most) Universal Systems began as House Systems, and can still be listed here in that case.
Contrast House Rules, which the local Dungeonmaster sometimes uses to circumvent System Rules that are not agreeable to them and/or their players.
Examples (by original publisher name):
- AEG: The D10-based system used for Legend of the Five Rings and 7th Sea. Both used the same basic die rolling mechanic, but were otherwise quite different.
- Chaosium: The Basic Roleplaying system is an interesting case: Chaosium mutated the original RuneQuest into a half-dozen systems with the same core mechanics (percentile skills and the same seven stats, more or less), and collected most of the variations into one system with numerous options.
- Except for Pendragon, which changed too radically.
- Mongoose's version of RuneQuest is just different enough from Chaosium's system to avoid lawsuits, but thanks to the first edition's Open Game License became the basis for other variations, mostly fan-made.
- Eden Games: The Unisystem.
- Fantasy Flight Games: The d10 system of Warhammer Fantasy Roleplay and similar games in settings from Games Workshop.
- Game Designers Workshop: The rule system from Twilight: 2000 second edition became their house system, used in Traveller: The New Era, Cadillacs and Dinosaurs, and Dark Conspiracy.
- Green Ronin: The AGE System, originally developed as Fantasy AGE for use with Dragon Age, it was also adapted for modern day (called Modern AGE) andused in games based on The Expanse and Lazarus.
- Guardians of Order: The Tri-Stat System, used for Big Eyes, Small Mouth among others.
- Hero Games: The Hero System is a textbook example of a single game (Champions) evolving into a House System (as used in the original editions of Star Hero, Fantasy Hero, Justice, Inc., Danger International, and Robot Warriors), and then back into a single Universal System game. Most of the older side-games were revived during the 5th edition era as genre-advice sourcebooks.
- Margaret Weis Productions: The Cortex and Cortex Plus systems were used for several licensed games, including Battlestar Galactica (2003), Firefly, Supernatural, Leverage, Smallville, and more. A separate Cortex rulebook was also released, making this a Universal System as well.
- Modiphius Entertainment uses the 2d20 System as a house system for licensed games based on works as diverse as Conan the Barbarian, Dune, Fallout, John Carter of Mars, and Star Trek.
- Monte Cook Games: The Cypher System began as a house system for Numenera and The Strange, before being expanded into a full Universal System.
- Palladium Books: The Palladium or "Megaversal" system.
- Pelgrane Press: The GUMSHOE system is Pelgrane's house system, but has expanded into use by other publishers as well.
- West End Games: The D6 system, which was initially used for Star Wars and Ghostbusters before being expanded into a Universal System.
- White Wolf has several:
- Wizards of the Coast: The d20 System was used as a house system (for, for example, Star Wars d20, d20 Modern, and Gamma World) in addition to its use by other publishers as a Universal System.