One of the points that Sinofsky made was that Windows 8 apps would work seamlessly together. While that always sounds nice in theory, it usually just means that the hooks are there for developers to take advantage of--either through application services in the OS or between apps. For Windows 8, Microsoft has built in the services, and any Windows 8 application takes advantage of them by default. In practice, what that means is that, in this example, if you want to, say, share a link from your Web browser to a friend via email, the "share" service brings up the apps, making it easy for you to simply select email and start to address a recipient. It's a fairly easy (trivial?) example, but the next slide shows a little more power.
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