Originally the source code for the .NET runtime was only available via Visual Studio 2008. The IDE downloads the source on an as-need basis while debugging an application. There is now an option to download the source from the Microsoft Reference Source Code Center, if you are a Windows user. Besides coming in a MSI package, there are some licensing restrictions developer need to consider.
Before we get into the EULA, a quick update on what's available and what's not. The core of the .NET, the Base Class Library is included. As are WinForms, WPF, and WebForms. Most of the non-GUI libraries such as System.Data are not available yet, but may become so in the future.
The .NET source code is available under the Microsoft .Net Framework Reference License. InfoQ cannot provide legal advice, but we would like to point out a few interesting sections.
First is a section that shows Microsoft is still very Windows-centric in its thinking. While they have been loosening up some cross-platform restrictions, they are not willing to give an inch to anyone they see as a competitor. This means Mono team members should not even consider looking at this code and anyone working on Linux itself should think twice.
"You" means the licensee of the software, who is not engaged in designing, developing, or testing other software, for a non-Windows operating system, that has the same or substantially the same features or functionality as the software.
Since this is a reference use license, it would be good to see how Microsoft defines the term "reference use".
"Reference use" means use of the software within your company as a reference, in read only form, for the sole purposes of debugging and maintaining your products to run on a Microsoft Windows operating system product. For clarity, “reference use” does NOT include (a) the right to use the software for purposes of designing, developing, or testing other software, for a non-Windows operating system, that has the same or substantially the same features or functionality as the software, and (b) the right to distribute the software outside of your company.
Again, their motives are clear. The source code release is not the result of a new sense of openness; it is for the practical benefit of developers targeting Windows.
And Microsoft did pretty much admit the source code release was unavoidable. Steven Tewils showed, the source was pretty much in the wild anyways. Releasing the source code really meant just releasing the comments.