Hookblade

The Hookblade was a modification to the hidden blade adopted by the Assassins of Constantinople. Upon his arrival in the city, Ezio Auditore da Firenze learned of this advancement from them, and also began to use it in both battle and travel.

Use
The hookblade was designed to make travel quick and easy, and was used in conjunction to ziplines planted throughout the city. It could also be used in several acrobatic movements, such as for flipping over enemies to avoid a fight, or swinging up vertical surfaces.

The hookblade could also be used as a weapon in combat, wherein Ezio pulls enemies in for a close-ranged attack.

Trivia

 * According to the June 2011 edition of GameInformer, Assassin's Creed: Revelations will feature a new control system. Pressing "Empty Hand" button (B on the Xbox 360, O on the PS3 and Shift on the PC) will now trigger the Hookblade.