Grapple Guns are hi-tech pistols that fire small grappling hooks on monofilament wire. Once the hook is secure, a button press will activate a powerful motorized pulley system that will allow the user to make a quick ascent to a rooftop. Variations of this gadget ares used constantly by Batman and the rest of the Batman Family.
It can also be used offensively to pull people or objects. Sometimes this requires a different attachment, like the Bat-Claw.
The Grapple Gun has become their most indispensable tool. With it Batman and his associates can scale ascend buildings in the absence of flight. But one means is as a means of travel, by swinging off of a fired line. They can slowly descent from high heights or save themselves from a fall or drop. They can use the grapple to grab objects or people. In desperation they can fire the grapple as a nonlethal projectile weapon.
Early versions of this gadget, such as the Batpoon or harpoon gun rifles featured no motorized pulley system, Batman had to physically climb the rope once fired. Batman rarely used such devices, typically justing using a Batarang as a hand thrown grappling hook.