Under System 6, fonts and desk accessories had to be moved around using a special tool called the Font/DA Mover.
The Font/DA Mover was just one of two font/desk accessory apps. Its sibling was the somewhat more able Font/DA Utility, which allowed you to rename files. (Similar third-party utilities, such as suitcase (then from Fifth Generation) could also do the deed.
Today, fonts are moved around with the mouse, in the Finder, or (as of Mac OS X 10.3) using Font Book.