The Multics OS has gone Open Source.
Now, you may be wondering , what is Multics (Multiplexed Information and Computing Service), and why is it significant? True, it doesn't run on any current commercially available system, but it was one of the influences for Dennis Ritchie when he worked on Unix (originally Unics, which stood for Uniplexed Information and Computing Service), which in turn heavily influenced Linus Torvaldes when he developed Linux, and also probably influenced both DOS and Windows, and certainly OSX.
http://www.theregister.co.uk/2007/11...code_released/