Pyxis 2.0 is the latest OS from Skewworks. Written in .NET MicroFramework and run on ARM processors with the .NET MicroFramework, this OS is completely free and open source. Creating apps for this OS is done using Visual Studio. You can get an express version free from Microsoft.
Thomas Holtquist the father of the project insists on referring to Pyxis 2.0 as an operating environment since the platform doesn’t really qualify for an operating system label since it’s missing some components such as User Access Control, according to one member of the .NET Micro Framework team.
Initially developed for the resource-challenged Arduino platform, Pyxis 2.0 is now capable of running on larger .NET Micro Framework devices, as you will be able to see in the two videos embedded at the bottom of this article.
More Info: Download