Essentially robots with wheels, with follow predetermined paths. They are not necessarily very intelligent, and often follow a magnetic, or optical strip on the floor.
Good examples are Factory Robots, the Manchester Airport Cleaning Robot and the Yo-Sushi Drinks Tray Robot. They are great for repetitive journeys and some attempts have been made to get these and other more intelligent counterparts to go over vast distances in the DARPA Grand Challenge.
Time to build your own robot! Using a Raspberry Pi with parts and some time, you can use my book to learn how to make and program a robot with automatic behaviours.