A cable tipped with a magnetic claw, fired by Enterprise NX-01 and its shuttlepods to seize and haul in objects in space in the years before Earth ships carried tractor beams.
The grappler is a metal line with a magnetic effector at its end. NX-class starships carry two, launched from the underside of the hull, and shuttlepods have a smaller one aft. It does the job later done by the tractor beam, a technology Earth does not yet have in the 2150s.
Enterprise first uses it in Broken Bow to capture a Suliban cell ship. In Breaking the Ice it fails to hold a shuttlepod that has fallen into a chasm on a comet, and a Vulcan ship finishes the rescue with a tractor beam. In Sleeping Dogs it reels in a shuttlepod hijacked by a Klingon.
In The Augments the grappler becomes a weapon, tearing a nacelle from a pursuing Klingon battle cruiser. Similar devices are used by other species, including the Pakleds in Lower Decks.