Back in 1987, at my first job at Hewlett-Packard, they had a little robot that would deliver mail. This was their plant in Loveland, CO, I believe it was the first non-California site HP opened.

Along the main hallways there was some sort of retroreflective tape laid down, and the robot, which looked like and equipment cart, would follow that tape. At every stop it would sound a chime and the secretary for that section would come out and retrieve a bundle of mail and distribute it to their people.

Super simple implementation, but it worked quite well for what it did.