Today Apple surprised us by finally making Swift an open source project.
At Swift.org you can find all the information about it.
4 main projects are being made public:
Compiler and Standard Library, comprised by Swift itself and a repository of documents related to the language's evolution.
Core Libraries, comprised by the foundation libraries,
Package Manager (!), comprised by the package manager itself and swift-llbuild, the build system that the package manager uses internally.
Cloned Repositories, comprised by the LLVM, Clang, lldb and CommonMark projects for Swift.
Apple says this is all available on Github, but it isn't just yet. However, this is huge. We already know the implications of Swift being open source, and now that it is a reality, there's nothing left to do other than start cracking on it!
Read everything at Swift.org.