Microsoft/dotnet on GitHub
Microsoft - .NET Framework Blog
John Robbins' Blog - How Many Secrets do .NET PDB Files Really Contain? John Robbins' Blog - PDB Files: What Every Developer Must Know
Microsoft - .NET Framework Blog - Opening up Visual Studio and .NET to Every Developer, Any Application: .NET Server Core open source and cross platform, Visual Studio Community 2013 and preview of Visual Studio 2015 and .NET 2015