That's all just one feature, which Apple dubs "Handoff." Continuity goes beyond that, by making your devices aware of each other in different ways. For example, when your Mac doesn't have a Wi-Fi connection, it will be able to automatically join a cellular hotspot created by your iPhone. Calls to your iPhone will ring on your Mac; SMS messages — that's right, not iMessages but those from your "green bubble" friends — will appear on your iPad and Mac; and you'll be able to initiate calls and texts from your Mac as well.
That Handoff feature is pretty cool, but is it only limited to Apple apps?
Nope, third-party developers who want to take advantage of Continuity will have that option. Apple is providing a framework for developers who want to have their apps talk to each other on iOS and the Mac. Obviously we'll have to wait to see what kind of clever ideas developers come up with to get the most out of this functionality.
What is CloudKit?
Most users won't really see the direct implications of CloudKit: It's a developer-facing tool that makes it easy for them to create a server-side app to support their iOS or Mac app. So, for example, if a third-party app requires something like push notifications, Apple will now provide an out-of-the-box system for supporting them, along with a data store and more. Basically, CloudKit will make it easier than ever for app developers to create complex client-server interactions, which in turn means better reliability and consistency for end-users.
What else will iCloud be used for?
Here's the thing: There are a lot of places where iCloud is clearly key to a piece of technology — some of the Continuity features Apple demoed, for example, work only when you're logged into iCloud on all your devices. Over time, Apple has come to rely more and more on iCloud as the unifying platform for its devices, starting with Messages and FaceTime and continuing in iOS 8 and OS X Yosemite as the two operating systems work together seamlessly. Sometimes the use of iCloud in those features isn't explicit. But it's clearer than ever that iCloud will be a crucial link in Apple's ecosystem.
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