When you think of dependable operating systems, do you think of Microsoft? If you've spent a lot of time with Windows, your answer to that is probably no. Nevertheless, Microsoft has been working away on an operating system for years now (since 2003) that would emphasize reliability via a tightly managed code kernel. Focused primarily on research applications, and a product of Microsoft Research, you can now download the source code and more from Microsoft's open source project hosting site
Codeplex. So what does Microsoft have in mind?