FUDGE is a generic tabletop roleplaying game system created by Steffan O'Sullivan, with many variations, including the popular Fate ruleset. It has a unique dice-resolution system using custom dice, called Fudge Dice, or dF. A fudge die appears on each dice card, they are fudge colored.
Fudge dice have six sides, two blank, two showing a + (representing +1) and two showing a - (representing -1). A set of dice are rolled (normally 4), and the values totalled. Positive values represent success, and negative values represent failure, with the size of the roll showing how dramatic a success or failure occurred.
The average roll, on any number of fudge dice, is always zero. So this scheme makes it very easy to figure out bonuses and modifiers. A modifier of +1, say, means that on average the result will be a mild success. A modifier of -3 makes it very unlikely the result will be anything but a failure.