What devices can I watch Apple's streaming TV service on?

Apple's streaming TV service, though not yet officially announced, is expected to launch in September and will likely be viewable on all the same devices that the recently announced HBO Now is compatible with. This means iOS devices including the iPhone, iPad and iPod Touch, as well as the Apple TV. You will likely be able to view it on your Mac desktop and laptop as well. HBO Now will apparently be viewable on a PC, but that remains to be seen for this streaming service.