Instant messaging
Barry Appelman is recognized as being the father of the "buddy list" and AOL instant messenger. Companies had been using crude forms of Instant messaging within their own networks for over forty years, but the idea of presence, i.e. who is logged on at any given time, was non existent. It was not until Appelman, and his colleagues at the Thomas Watson Research Center, first began to write programs on the mainframe system letting each other know when they were actually online, that modern day Instant Messaging was born.