Re:Guide to the CoreCLR Source Code
by matthewwarren on Saturday March 25, 2017 @12:05PM
(#13956242)
Oh yeah, I'd forgotten about 'Reference Source', although AFAIK that's only the equivalent of CoreFX, not CoreCLR
You still might quibble over "entire" .NET Framework, but a lot of the .NET Framework is open source in addition to .NET Core.