The Netbook of Ghosts

From the introduction: Ghosts are merely restless spirits whose passing onto the next world is prevented for a number of reasons: for instance, the person may have died with an urgent need to pass on an urgent message, or to accomplish some unfinished task. In other cases, the ghost may be angered over its betrayal and murder in life, and cannot rest until the one who committed the crime is properly punished. A ghost might also, through its misbehavior in life, find itself bound to an unhappy existence between worlds until it finds some sort of way to atone for its actions. A relatively weak spirit might remain under the domination of a greater creature, tormented and unable to rest until the creature is destroyed. Finally, a ghost may just not know that it has died.