Alternity is a science fiction role-playing game (RPG) published by TSR in 1997.

which represent the numbers needed to achieve Ordinary, Good, or Amazing successes in an action round respectively.

Unlike many other systems, actions are determined by a control die and situation dice.

The total of the rolled numbers is checked against character's action, skill, feat, to indicate a success or a failure.

Depending on how far below the skill score the player rolled, there are 3 progressively better layers of success and 2 levels of failure.

Life points, called 'Durability', are categorized into Stun, Wound, and Mortal damage.

The Gamma World campaign is an d20 Modern expansion by Sword & Sorcery Studios (White Wolf).

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.

Several books were published under the Alternity banner as core products, accessories, or under specific campaign settings.

In addition to the general Alternity line of products, four campaign settings were published, each with their own books: