A large space-based launcher built by the alien engineer Tash, which locks a ship in a graviton surge and throws it hundreds of light years in a few hours.
The catapult appears in the Voyager episode The Voyager Conspiracy. Tash, a traveller stranded far from his own people, has spent years building the device, which is powered by a tetryon reactor, and Janeway agrees to help him finish it in return for a turn.
Seven of Nine, who has been absorbing the ship's records directly into her cortical implants, notices that the reactor resembles the one in the Caretaker's array. Overloaded with data, she builds one elaborate theory after another, convincing Chakotay that Janeway deliberately stranded the ship and then telling Janeway that Chakotay is plotting a Maquis attack.
Once the Doctor identifies the cause, the conspiracies evaporate. Tash's launch succeeds, and Voyager follows, cutting about three years from its journey.