A space-time navigator was used to "navigate a course through space and time". A side effect of using it allowed the user to predict future events.
A space-time navigator was located in room 413 of the offices of MacDonald, O'Brien and Withers. The thief Darrakhaan broke into the offices to steal the navigator, which was fashioned as an amulet. However, he was stopped by the Eighth Doctor, who used the navigator to predict Darrakhaan's actions and trap him in a time loop. (PROSE: After Midnight)