and twenty-sided dice. It does not use the popular ten-sided die, perhaps to help distinguish it from the competing World of Darkness and the Trinity role-playing game, published by White Wolf Game Studio. The probability curve created by the addition or subtraction of a d20 and another die is shaped like a plateau, with two straight lines on both ends of the flat region. This is intermediate between the totally flat probability curve rolled by rolling a 20-sided die and the bell-shaped curve produced by die pool systems. Published products Several books were published under the Alternity banner as core products, accessories, or under specific campaign settings. Core products These products presented the basic rules and information about the Alternity system. Introductory Box Set – A box set including all the basic information for players and gamemasters to learn the Alternity rules. Player's Handbook – Included all the rules for players and player characters. Required to play. Gamemaster Guide – Included all the rules for gamemasters and session preparation. Required to play. Fast Play – An abbreviated form of the rules to ease players into the game. Campaign Kit – The kit included a gamemaster's screen and a booklet of record keeping forms. Accessories These products were not tied to any of the official campaign settings but could be used with them. Beyond Science: A Guide to FX – An exploration and reworking of the FX abilities (a sci-fi version of magic) in the corebook. Dataware – The guide to computers, hacking, and robotics. Mindwalking – The guide to psionics including revisions to the rules from the corebook. Starships – The guide to interstellar ships and travel. Tangents – This book explored the concept of parallel realities in the same vein as the 90s television show Sliders. Campaign settings In addition to the general Alternity line of products, four campaign settings were published, each with their own books: Star*Drive – A space opera setting. Dark•Matter – A setting similar to The X-Files television show. Gamma World – An update to the classic post-apocalyptic game setting. StarCraft Adventures – Based on the popular computer strategy game by Blizzard Entertainment. This setting used simplified "fast play" rules rather than the full Alternity rule set. References External links The official Alternity fansite Role-playing game systems Role-playing games introduced in 1998