Gravity lift

The Gravity Lift is Covenant graviton technology used to either levitate objects into the air via an amethyst, sparking circular beam that is refractive to plasma, or to safely drop troops in the same fashion. However, the polarity of the lift needs to be reversed in order to switch from the two different functions. They are projected from both the underside of most Covenant ships and Deployable Lookout Towers.

Appearances
Gravity Lifts are seen twice in the game Halo: Combat Evolved. These scenes both involve the Master Chief and the Covenant CCS-class battlecruiser Truth and Reconciliation, which can be seen projecting the lifts in the levels Truth and Reconciliation and Keyes. The gravity lift belonging to the High Prophet of Regret is also seen in Halo 2 throughout the first few levels as it overs over New Mombasa.

Gravity Lift as a weapon
The Gravity Beam is a newly introduced weapon that Covenant ships use. While a Gravity Lift is usually used for ferrying troops and supplies, it can also be used as the interesting yet devastating gravity beam.

The shipboard weapon was first seen in the last cutscene of Regret as the Master Chief escapes a Covenant Assault Carrier opening fire on the temple with it's grav beam. To prove that the Gravity Lift plays a role in transforming itself into the gravity beam as a weapon, look at the circumference, which is the outer wall of the beam, and you'll see those same oscillating purple lines on the wall of the beam. As a matter of fact the outer wall, the circumference of the grav beam, has the same purple color of the ordinary gravity lift.