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. Its other function was to reverse time over a large area. The core was a blue cube, without which the Freedom 1b was inoperable. (PROSE: Freedom)
The Master set up the Freedom Corporation as part of a plan to escape if he was captured. When he was captured, he had his servant, Gerald Gooder, announce the Freedom 1b. The Third Doctor and Jo Grant investigated and Gerald activated the machine, transporting him to the the construct. The Doctor and Jo followed, becoming trapped as well.
When the Doctor and Jo stayed missing, 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 intervened, freeing the Doctor and giving him back his TARDIS as well as his knowledge of how to work it. The Doctor reversed the Freedom 1b, saving Earth. (PROSE: Freedom)