Andy Hertzfeld, one of Apple's original Macintosh software architects, wrote Switcher after seeing John Markoff use a terminate-and-stay-resident program on an IBM PC in October 1984. By the end of the year he had a working prototype, and he soon demonstrated it in public. Both Microsoft and Apple wanted to purchase the utility. Hertzfeld chose the latter because of his belief that Switcher should be bundled with the Macintosh system. Apple offered more money (US$100,000 plus royalties) and the company planned to ship Switcher with the Macintosh 512K. The first official version of Switcher appeared in April 1985.
Switcher works by designating a number of fixed slots in memory into which applications could be loaded. The user can then switch between these applications by clicking a small button on the top of the menu bar. The current application horizontally slides out of view, and the next one slides in. Though awkward, this approach does fit well with the existing system's memory management scheme, and applications need no special programming to work with Switcher. This early work on Switcher led to the development of MultiFinder by Apple system software engineers Erich Ringewald and .