At last year's WWDC Apple announced a brand new programming language in the form of Swift. The hope was that it would make programming easier and faster, as well as making a better final product. Today, Apple announced a successor in the form of Swift 2.
Apple believes that Swift should be used by everyone, and available everywhere. So to make that happen, it's made Swift 2 open source. Compilers and libraries for OS X, iOS, and Linux will be available by the end of the year.