A new operating system, code named Barrelfish is being developed by Microsoft research labs and ETH Zurich in Switzerland. This operating system is being built with multi core operations foremost in priority. It is supposed to be extremely scalable and able to function on a very wide range of hardware. You can download the current snapshot of it on their site and dig into the source code, released under a 3-clause BSD style license. If you would like to learn the primary differences between this OS and Windows or Linux, you can read this PDF.