http://www.barrelfish.org/
Barrelfish is a new open source OS, being co-developed by ETH Zurich in Switzerland, and Microsoft Research Cambridge in the UK. The OS itself is being designed to allow maximum scalability for the ever increasing number of CPU cores that are going to become commonplace over the next few years.
It's still a long ways from being a useable operating system, but it's in development, and there IS a snapshot of the current system available for download. If you are a coder, or just an OS geek, check it out.
If nothing else, it's an interesting read, and definitely a cool concept.