When he was just 25, Doug Engelbart had an epiphany about his life's purpose. "If you could do something to improve human capability to deal with the increasing complexity of the world," he thought, "then you'd really contribute something basic." Almost 20 years later, Engelbart unveiled the result of that idea: a graphic computer system, controlled by a special keyboard and something called a mouse, that would let people work together on documents, manipulate complex ideas, even from far-flung locales.