[Longhanks]

It's just the Swift language itself that is open source and a few libraries. Most of the OS X layers above BSD are still closed source.

It's not "more open" than C# and .NET in that regard.

[Twisell]

Sorry if I was wrong I absolutely now nothing about c# & .net.

Does it mean one could actually review code and fork theses languages too if need be?

[Locke1689]

Certainly: https://github.com/dotnet/roslyn