Most of the 'Darwin' open source releases on opensource.apple.com are not under any variant of the GPL. However, they are only provided for OS X - the iOS section only has a short list of LGPL projects, and ARM code is often stripped out; new projects are never added, even rewrites of older code that was open source (launchd, discoveryd); several projects cannot be compiled without some work dealing with missing header files; and some projects (kernel extensions) have over the years had entire files redacted to blankness, or been removed from future distributions altogether. In other words, it very much feels like a legacy thing.