Fifty years ago today, on December 9th, 1968, Douglas Engelbart presented the Mother of All Demos, introducing the oN-Line System (NLS) to the world and with it then novel concepts such as the computer mouse, hypertext or remote collaborative document editing. In my humble opinion it is probably the most important moment of HCI history in the 20th century.
Watching this today, it is astonishing how seemingly simple and (nowadays) familiar technologies such as the computer mouse had to be explained from the ground up back then. If you got an hour and a half to spare, spend some time (re-)watching the event (now available on Youtube, but still also available at Stanford), or read about its importance and legacy at Wired or Ars Technica. Wired also shared a fascinating look at how they pulled it all off.