Project Indigo was UNIT's first experimental teleportation device developed in 2009. It was reverse-engineered from Sontaran technology which was left behind following their failed invasion of Earth in that year.
The first person to successfully field-test the prototype was Martha Jones during the Dalek invasion later in 2009. Prior to this, Jack Harkness warned Martha against using it given its experimental nature. He told Gwen Cooper and Ianto Jones it had no coordinates or stabilisation. (TV: The Stolen Earth) Though trying to get to an Osterhagen Station, she was instead briefly diverted to Atlantis by a temporal crisis. She took notes of the coordinate, but then immediately activated Project Indigo again, thinking to herself that "there's no place like home". (GAME: Lost in Time)
This worked, with Project Indigo tapping into her mind and taking to her mother's house, "the place [she] most wanted to be". Martha later used the device again, to teleport herself to the vicinity of the Osterhagen base in Germany, where it was discarded by the door of the detonation control chamber. (TV: Journey's End)
Jac used Project Indigo to rapidly transport Jo Jones, Rani Chandra and Rio from the Amazon jungle to UNIT's base at Gibraltar. (AUDIO: The Turn of the Tides)