Freedom 1b

Freedom 1b was a time travelling device created by the Master via the Freedom Corporation.

Abilities
Freedom 1b was a squat, mushroom-shaped device. It had at least two functions. It could be used to transport a person through time and space, while staying still itself. It's other function was to reverse time over a large area. The core was a blue cube, without which the Freedom 1b was inoperable. (ST: Freedom)

History
The Master set up the Freedom Corporation as a way to escape if he was captured. When he was captured, he used his servant, Gerald Gooder to announce the Freedom 1b. When the Third Doctor and Jo Grant investigated, Gerald activated the machine, transporting him to the the Construct. The Doctor and Jo followed, trapping them as well.

When the Doctor and Jo didn't return, Brigadier Lethbridge-Stewart negotiated with the Master for their return. He brought them to the Freedom 1b and activated the second part of the plan, which turned back time for Earth. This was so destructive that the Time Lords had to intervene, freeing the Doctor, giving him back his TARDIS and his knowledge on how to work it. The Doctor then was able to reverse the Freedom 1b, saving Earth. (ST: Freedom)