– Andy Hertzfeld, who wrote much of the original Mac operating system, is still heavily involved in technology and Macs. When it comes to the latter, he’s both a historian and a fan. Hertzfeld is also an advocate of the open source movement. He started at Apple in August 1979 as Apple employee #435. He worked on the core operating system and the User Interface toolbox, as well as most of the original desk accessories. After leaving Apple he went on to co-found three companies: Radius (1986), General Magic (1990) and Eazel (1999).