I would have to vote for philosophical skepticism as the most important "invention" (if one thinks of invention as fabrication rather than discovery, as it is more archaically meant) of the past two thousand years. The notion that there is a "truth behind" things and a "bottom" to the matter has instilled in all of us, whether scientists, philosophers, theologians, or lay people, a maniacal obsession with improving our explanatory capabilities. As such skepticism can be seen as the driving force behind science and technology, modern conceptions of faith, the soul, and the other. Of course, one might argue that skepticism has been around for longer than two thousand years; but its characterization as a fundamental problem to be contended with before any constructive work can be done seems to me a peculiarly modern invention, a defining feature of our intensively self-conscious, post-Cartesian world.
President and CEO of Learn Technologies Interactive in New York City