One of the most significant announcements at Apple’s Worldwide Developer Conference (WWDC) in June was the plan to open source the firm’s Swift programming language. This would have been entirely unremarkable for most companies, but for one whose business model relies so heavily on walled gardens, it was a major sign that even Apple has to adapt to the realities of modern software and open systems. The company has kept its promise, and this could open the floodgates for cross-platform applications written in Swift. While Apple is not straying so far from its roots as to port Swift itself to Android, Linux or Windows, open source availability of the standard Swift library and compiler, on the Swift.org website, will enable…