The issue is not so much technical as it is about legality. Codesign is itself open source (Darwin), but Apple TOS forbids you from building OSX/IOS apps to be

The issue is not so much technical as it is about legality. Codesign is itself open source (Darwin), but Apple TOS forbids you from building OSX/IOS apps to be distributed on the App Store on non Apple Hardware. I guess you could do it anyway, but I don't think people would risk it for the price of a mac mini...