The Singularity project was started in 2003 as a fundamental redesign of how operating systems work. From the ground up everything is based on the concepts of isolation and verifiability.
Processes are highly isolated from one-another. Communication is done strictly via type-safe channels, shared memory of any form is not allowed. Processes are "sealed", meaning they cannot dynamically load or generate code. This has the advantage of making virus injection virtually impossible, at the cost of not being able to use dynamic link libraries or meta-programming techniques.
Other than a small part of the kernel, the bulk of Singularity is written in the type-safe language Sing#. Instead of platform specific assembly languages, Singularity uses .NET's IL as the lowest common denominator. Singularity will not even try to load unmanaged applications.
The first 2.0 release includes the full source code tree and a bootable CD image. A Virtual PC file is also available in this release.
In an unusual move by Microsoft, Singularity is soliciting patches and offering full developer rights on CodePlex.