Grail is a library of quest information designed to provide that quest information to other addons to make their decision processing easier. For example, an addon like EveryQuest or TourGuide would be able to make use of Grail's knowledge to determine if a quest has been completed, whether the character can obtain a quest, what reasons the character cannot obtain a quest (lack of level, wrong race, wrong class, not enough reputation, has not completed a prerequisite quest, etc.), the location to obtain or turn in a quest, the amount of reputation awarded from completing a quest, whether a quest counts towards an achievement, etc.