Google hosted their dev page for .NET. I’m not sure if their library is only for Windows phone or Window desktop OS also. But anyway, they have it. Where their source code or binaries are hosted is NuGet gallery.
What is funny is that they hided its link from their Products page although it’s displayed under it.
For C++, it’s also hidden. They have it hosted at GitHub.
Although each service API page is on the same developer.google.com site, their developer’s guide and source code are hosted at GitHub