Cruciform

The Cruciform existed during the Last Great Time War. The Dalek Emperor took control of the Cruciform. The resurrected Master was so scared, he ran away and used a Chameleon Arch to turn himself into Professor Yana and hide near the end of the universe. (TV: The Sound of Drums)

The Tenth Doctor said the Cruciform fell at the same time that Gallifrey was burned. (COMIC: The Forgotten)

Behind the scenes
The Cruciform hasn't been confirmed to be either a location, a weapon, a ship or some kind of object. It has only been mentioned, not described. The word 'cruciform' means “cross-shaped”, and is, amongst other things, a type of real-life screwdriver.

i think cruciform is the operator base of sky trenchs master said he saw dalek emperor invade cruciform maybe after master escape daleks took years worked the station,took control of sky trenchs and attack arcadia

The Crucible, the Dalek space station that appeared in The Stolen Earth/Journey's End, has been said to be in no way connected to the Cruciform.