Barrel fish
Barrelfish is an experimental operating system that is being developed by Microsoft Research in collaboration with ETH Zurich . Barrelfish is sometimes dramatically different from current operating systems because it was specially designed to ensure the highest possible execution speed on multi-core processors as well as broad support of different computer architectures . Much of the developers at Microsoft Research were involved in Singularity before Barrelfish . The source code of the operating system is under the MIT license and can be obtained free of charge.
The current version was published in December 2014.