The Claw, or the Rapier, is a long bladed sword characterized by the large and simple hilt, which provides protection for the hand wielding it. It is mainly used for thrusting and stabbing the wielder's enemies, but it is somewhat capable of slashing and cutting - although it's not its main purpose and much more difficult to use this weapon effective that way. The blade itself is longer than the normal sword and much lighter. The blade is made of ebony.
The blade's point is sharper than the sides of the blade itself.
The origins of this blade are known only to some. The blade was created by the Daedric Prince Molag Bal, and cast it on Nirn for unknown reasons. The sword came into possession of various nobles from generation to generation, until it was stolen by Jack Jackson in the 6th era of industrial Tamriel, when he stole it from an old and wealthy merchant.
He used the blade since then, until Sander Lafayette stole it from him when fighting him in Leyawiin. As such, the blade is currently wielded by Sander Lafayette.
Sander Lafayette, in the second part of the second chapter claims that the essence of a daedric entity originiating from Molag Bal's realm of Coldharbour made it special, as the Claw itself was a simple blade of Ebony.
The Claw, apart from its seemingly normal look, has various powers that can be utilized in battle against both normal people and others, like lycanthropes, vampires, and Daedra.
The sword has the unique ability to set enemies ablaze with bits of black fire, which are hard to extinguish. These do much more damage than normal fire, and is handy for fighting Vampires.
It's second ability is that it may slow one's health regeneration, making it diffiicult for Daedra and Vampires to regenerate wounds / limbs.
It can also give the wielder strange and vivid hallicunations, suggesting it might have a mind of his own - it even has the ability to speak to its wielder, in a low, raspy, and demonic sounding noise - although this happens rarely, the voice only speaks in strange and obscure riddles and rhymes.
All of these powers are passed on to the Saw Cleaver upon the beginning of the events of Ashes of the Past.