During the 2015 WWDC keynote, exactly one year after Swift was announced, Apple made another astonishing announcement: Swift will be open source!
Apple will release a first Linux version, which is completely decoupled from the Cocoa Foundation, and move the development and evolution of the language to the hands of the community.
As mentioned, the first Linux release will be done by Apple, but in the future, we can see Swift running everywhere: Windows, Android, and so on—everywhere the community of developers wants to create a version.
In early December 2015, Apple finally kept its promise and released the source of Swift on GitHub: https://github.com/apple/swift.
Apple also released a long-awaited packed manager, a sort of official CocoaPods, called Swift Packet Manage, which will help release modular software without using Xcode.
The Linux version is still in its infancy and is not ready for production; nonetheless, it's good enough to start experimenting...