Fantastic Adventures in Tabletop Entertainment, is a generic role-playing game. Fate is currently based on the FUDGE gaming system. It has no fixed setting, traits, or genre and is almost entirely customizable. However, it is designed to offer the least possible obstruction to role-playing by assuming that players do not want to make large amounts of dice rolls.
While FATE uses FUDGE's verbal scale and four three-sided dice, it breaks from most other role-playing games by doing away with mandatory traits such as Strength and Intelligence, and substantially reworking the "experience point" mechanic. It instead assumes that every character is "average" and allows exceptionalism to be defined through an Aspect system. A player may choose, for example, to take an Aspect in Brawny (or Muscle Man or Wiry Strength) and choose to spend Aspects to gain a temporary bonus in a relevant situation. Aspects may also be taken in possessions, e.g. the character Indiana Jones might have the Aspect "Whip and Fedora". The fact that Aspects can be anything integral to the character allows for a degree of melding of mechanics and role-playing difficult in most other gaming systems.
An important and original concept in FATE is, Aspects are not intrinsically good or bad: they are simply descriptive, up to the level of detail the player requires. In addition to the obvious direct character help in most cases, the FATE system also provides a mechanism to reward the characters when one of their Aspects has restricted their choices or landed them in some trouble.
(Quoted from the FATE RPG Wikipedia entry)
Fate has of late lost its use as an acronym and is usually indicated "Fate" with a capital "F". Since the release of Spriit of the Century, a good number of variants, some so far off the main branch they are no longer considered Fate proper by the original designers, have come out. The release of The Dresden Files RPG marks the first instance of what has been called "Fate 3.0", which is being actively developed as a new, generic system for release by Evil Hat Games.
Notable variations within the various Fate games typically are to do with the types of dice used (Cubicle 7's Starblazers Adventures and Legends of Anglerre commit to the 1d6 - 1d6 variant rather than the traditional Fudge dice), how damage or "stress" is handled, use of stunts (or not), and character advancement. An up-to-date summary may be found on the Fate wiki.