Project Indigo was Earth's first experimental teleportation device, which was reverse-engineered from the Sontaran teleport pod. The first person to test the prototype was Martha Jones. However, Jack Harkness highly disapproved of the device, saying that it hadn't been tested. Despite this, the device worked and teleported her to her mother's house. (DW: The Stolen Earth)
Later in The Stolen Earth Jack asks Martha what the the two numbers that are oscillating are (they are 4 and 9). Jack then goes on to say that the was all he needed to get his wrist teleporter to work, so one can speculate that Project Indigo was the prototype for the wrist teleporter that the Time Agency used.
