3D printing. The rapid printing of three-dimensional objects allows inventors without a lot of resources such as a machine shop to prototype their inventions. 3D printing also allows small businesses to create products and works of art that can compete with large businesses in terms of quality in design. Even without 3D models a business can still sell its products by selling the files for making the 3D items on-line so other people can print the items on their own 3D printer.
Many items can now be 3D printed from plastic, metal and even food can now be 3D printed. Hospitals are currently using 3D printing technology in such applications as prosthetics.
When it comes to 3D printing development what I am really excited about is working toward a 3D printer that can print other 3D printers. RepRap comes close because it can print most of it's own components. Once a 3D printer can fully print another 3D printer it would enable a lot of poor to be able to have access to cheaper products by owning their own 3D printer.