They are written by different teams (source: I know people who have worked on each team). They share things, of course. In fact, the "new" (as of a few years ag

They are written by different teams (source: I know people who have worked on each team). They share things, of course. In fact, the "new" (as of a few years ago) source editor in Xcode came out of Swift Playgrounds for iOS originally.