From Halopedia, the Halo wiki
Torsion drivers are a kind of weapon system employed aboard Forerunner warships. Torsion drivers are gravitic emitters (presumably emitting torsion fields) that can be employed as a delicate tool or a crude scalpel as the situation permits; in battle, they use their gravity generation to push and pull portions of enemy craft beyond the limits of their shielding and structural supports with discordant harmonies. This action rips apart the target vessel and exposes its vulnerable systems to concentrated fire by other weapons. Grapplers can be used in a similar manner to torsion drivers, though lack the power and range necessary for shearing enemy warships.
During war, the Didact crafted a weapon known as the stasis tension driver, created out of an array of repurposed torsion drivers paired in concert with quantum singularity generators and an array of projectors to generate localised space-time distortions.
Torsion drivers may have been employed by the rate of Miners in times predating even the Kradal conflicts. If UNSC speculation is to be believed, the recovered examples of the "gravity wrench" are believed to employ either scaled-down or archaic forms of the technology, and have been suggested to originate from this era.