Apple on Thursday released iOS 9, the latest version of its mobile operating system. Although more evolutionary than revolutionary, it has some useful additions. The good news is that iOS 9 works on much of Apple's existing hardware. If your device can run iOS 8, it should be able to run iOS 9. However, some of the software's features are available only on the newest iOS devices -- the iPhone 6s and 6s Plus, and the iPad Pro.