The restless dead are the remnants of humans who have unfinished business in the physical world. Some are relatively benign, while others are evil beyond redemption.
Each of the restless dead is unique and therefore only a few generalities can be mentioned. The restless dead are immune to cold and mind-influencing spells such as charm or sleep, like other undead. They cannot normally be turned, destroyed, or controlled by clerics. The restless dead are almost always found within a fixed area, whether it be a place important to them or the site of their demise. They will sometimes be guarding a treasure that was important to them in life. If they have cause to leave the site of their haunting in the course of their un-life (such as if their treasure is stolen), they may be turned as a 'Special' type of undead. The dead might be corporeal, semi-material, or completely non-corporeal.
The restless dead that have corporeal or semi-material form will normally be able to attack. Most commonly, they will attack by a means related to the way they died, though this is not an absolute. Attack may be physical, by means of a cold touch, withering, energy drain, strength drain, disease, or some other method. These restless dead will have hit dice, armor class, movement, and attacks as befits their form. Some will be hideous, but all will be otherworldly and strange. Some may be struck by normal weapons, while others can only be hit by silver or magical weaponry.
Restless dead may be exorcised. Sometimes, one can be rid of them by helping them finish whatever task or cause keeps them imprisoned in this world. At other times, the dead may be so confused or malevolent that this is impractical.
Not all restless dead are evil. When given help, some may even offer a boon in the form of a valued possession or curing touch. The restless dead will usually have the same intelligence and wisdom they possessed in life.