The gravitic anomaliser was a component of the TARDIS. It generated a localised field of artificial gravity around the outside of the vessel.
The Fourth Doctor used the gravitic anomaliser to help a Skonnan ship escape the gravity field of a nascent black hole. (TV: The Horns of Nimon)
The Tenth Doctor closed down the gravitic anomaliser prior to taking Martha Jones on her first trip in the TARDIS. (TV: Smith and Jones)