The Mother of All Demos, presented by Douglas Engelbart (1968)

From the Stanford page :

“On December 9, 1968, Douglas C. Engelbart and the group of 17 researchers working with him in the Augmentation Research Center at Stanford Research Institute in Menlo Park, CA, presented a 90-minute live public demonstration of the online system, NLS, they had been working on since 1962. The public presentation was a session of the Fall Joint Computer Conference held at the Convention Center in San Francisco, and it was attended by about 1,000 computer professionals. This was the public debut of the computer mouse. But the mouse was only one of many innovations demonstrated that day, including hypertext, object addressing and dynamic file linking, as well as shared-screen collaboration  involving two persons at different sites communicating over a network with audio and video interface. ”

YouTube link:

Douglas Engelbart died Tuesday at the age of 88. See also the NYTimes and Ars Technica related articles.