Although Apple had announced at WWDC 2015 that the Swift programming language was going to become open source, it took until today for the iOS, OS X and watchOS development software to move out of the auspices of Apple. A new website, Swift.org provides information about the open source project along with documentation and new user training.
The welcoming statement on the website says it all:
Swift is the brainchild of Chris Lattner, who is the senior director of Apple's Developer Tools Department. In 2010, he began taking ideas from Objective-C, Rust, Haskell, Ruby, Python, C#, CLU and other languages to create the new language. Swift was first unveiled at WWDC 2014.
The language will be open source under the Apache license, which says that developers can use the software for any purpose and even distribute modified versions of Swift without paying royalties to Apple. It's hoped that developers will begin to use Swift for development outside of the Apple ecosystem.