"The One-Roll Engine (or O.R.E.) is a generic role-playing game system developed by Greg Stolze for the alternate history superhero roleplaying game Godlike. The system was expanded upon in the modern-day sequel, Wild Talents, as well as the demonic supervillain game Better Angels, the Film Noir game A Dirty World, the heroic fantasy game Reign, and the free horror game Nemesis. A simpler version was used for Monsters and Other Childish Things. The One-Roll Engine is notable for its unique dice rolling system in which matched values on ten-sided dice (d10s) determine all variables of a check in a single roll. This eliminates, for example, the separate initiative, hit location and damage rolls common during combat in other systems.
The O.R.E. system uses a dice pool of d10s equal to the character's Stat and Skill similar to that used by Storyteller system, but the method to determine success is different. In the O.R.E. system, success is determined by die result matches, such as a pair of 8s. The Width of a roll, the number of matching dice, determines the speed (and damage, if in combat) of a roll, while the Height of a roll, the face up result on the matched dice, determines how successful an action was and location of a hit in combat. Shorthand notation for writing results is Width x Height, so a pair of 8s would be written 2x8 and three 2s would be written, 3x2.
Two special types of dice also come from Talent Powers, Hard Dice, which are considered to always have a value of 10, and Wiggle Dice, which the player can assign any die result to after the roll. The shorthand notation for Hard Dice is hd and Wiggle Dice is wd, so a Dice pool of six regular dice, two Hard Dice and one Wiggle Die would be noted 6d+2hd+1wd.
NEMESIS introduces Expert Dice, which may be used as normal dice, or the player can to select their value before the roll, but no two Expert Dice can be selected to have the same value. Expert Dice are also used as buffer against die penalties, where each Expert Die counteracts one die penalty, but then must be rolled as a normal die. NEMESIS also renames Wiggle Dice to Trump Dice. The shorthand notation for Expert Dice is ed and Trump Dice is td.
Reign also uses "Wiggle Dice", but uses the name "Master Dice" (shorthand notation "md"). In this setting any dice pool just could contain one special die ("md" or "ed") and can never roll more than ten dice at once. (Excess allows offsetting penalties while still resulting in an effective pool of ten.)
In Better Angels instead of their dice pools being based off traditional statblocks, each character has competing traits for various aspects like Knowledge, Generosity, and Honesty on one side and Corruption, Greed, and Cowardice on the other which shift throughout the game based on a character’s actions and personal development. Each player controls both their human character as well as the demon ’screwtape’ for the player to their right, with the demon picking half of their supervillain host’s sinful stats, superpowers, and demonic aspects during character creation. "Master Dice" appear as one of boons demons can tempt their hosts with as part of their plot to corrupt the souls of their well meaning hosts badly enough to enable them to be dragged to hell
The simplified O.R.E. used in Monsters and Other Childish Things only uses special dice for monsters. Normal dice in a monsters' pools may be sacrificed during character creation for special qualities, one of which, "Awesome", grants a die that works like an Expert die in Nemesis. Taking the Awesome quality a second time makes the die function like a Wiggle Die. Monsters does not use Hard Dice, but other special qualities modify rolls in specific, more limited ways. For example, "Gnarly" adds one to damage in combat rolls, while "Wicked Fast" adds one to Width for the purposes of determining speed.
Source: Wikipedia, "One-Roll_Engine", available under the CC-BY-SA License.