A sword forged by Munifican for Charlemagne to give to Prince Ogier of Denmark.
From Bullfinch's Mythology, Legends of Charlemagne, Chapter 24: Ogier the Dane:
Turpin in a solemn service implored the favor of Heaven upon the youthful knights, and blessed the white armor which was prepared for them. Duke Namo presented them with golden spurs, Charles himself girded on their swords. But what was his astonishment when he examined that intended for Ogier! The loving Fairy, Morgana, had had the art to change it, and to substitute one of her own procuring, and when Charles drew it out of the scabbard, these words appeared written on the steel: "My name is Cortana, of the same steel and temper as Joyeuse and Durindana." Charles saw that a superior power watched over the destinies of Ogier; he vowed to love him as a father would, and Ogier promised him the devotion of a son. Happy had it been for both if they had always continued mindful of their promises.
In Bungie's game Halo, there is an AI named after this sword.