On December 9th, 1968, Douglas C. Engelbart—along with 17 researchers from Stanford -- gave a 90-minute live public demonstration of the technology they'd been working on for the previous 6 years. It changed the face of technology -- and you can watch it in full here.
The presentation was the first time the computer mouse had ever been demonstrated. But there was more, too: that day they also showed off hypertext, object addressing and dynamic file linking, as well as a shared-screen collaboration involving two persons at different sites communicating over a network with audio and video interface.
It was mind-blowing then, and is insanely impressive now. [Stanford]