Building autonomous tools is my candidate for the most important invention.
Artificial complex adaptive systems, from robots to any type of autonomous agent, will change our world view in a qualitative way, comparable to the change brought by the use of thing-like tools.
Tinkering with tools has shaped our view of the world and of ourselves. For example, the invention of the pump enabled us to understand the mechanical role of the heart. Science was born when laboratory apparatus was used to select among mathematical theories of the physical world which one correspond most closely to reality. But all those tools have been lifeless and soulless things, and it is no wonder that our scientific world view has tended to objectify everything. Grasping the proper role of the subject pole of experience, through the invention of subject-like tools, may provide the key to a far wider world view.
With the invention of perspective, in the late Middle Ages, we shifted our collective Western experience one-sidedly into the object pole, leaving the subject pole out of the picture. We started looking at the world from behind a window, and a couple centuries later, in science, we attempted to take a God's eye view of the world. By now, we are coming around full-circle, with our science and technology providing us the means of exploration of the role of the subject.
We have only set the first steps towards building artificial subjects. Just as our current artificial objects are vastly more complex than the first wheel or bow and arrow, our artificial subjects will grow more complex, powerful, and interesting over the centuries. But already we can see a glimmer of what lies ahead: our first attempts to build autonomous agents has taught us new concepts. As a result, we are now beginning to explore self-organizing ecological, economic, or social systems; areas of study where thing-like metaphors hopelessly fail.