Moving apps from one display to another in Mission Control.
The third display: OS X Mavericks's AirPlay display was shown off pretty prominently on stage, but we'll still mention it here because it's such a neat feature. If your computer is powerful enough, you can drive not just two displays, you can also turn your Apple TV-equipped HDTV into a third, fully-functional display via AirPlay.
How powerful will your computer have to be? That we don't yet know, but I imagine Apple will release more information as the Mavericks release date inches closer.
Save your Wi-Fi passwords across devices
iCloud Keychain's big appeal is its password and credit card number saving, but I'm personally looking forward to Wi-Fi network and password storage. Come the fall, when you log in to a Wi-Fi network on your Mac, iCloud will remember the network and password in case you need to log in on a different Mac, iPhone, or iPad.
The new Reader
If you love OS X's Reader function in Safari, you'll probably enjoy Mavericks's improvements to the pared-down reading feature. Come the fall, Reader will ditch the hover-page for a separate screen bordered in cool grey.
Read multiple books at once
Coming from the single-screen view of iOS, reading multiple books at once sounds like crazy talk. But that's the advantage to having apps like iBooks on the Mac: multiple windows to view multiple books. Of course, iBooks makes no guarantees about giving you the multitasking needed to read multiple lines of text.
Calendar gets you where you need to go
We know that rich Corinthian leather and stitching effects are no more in the OS X Mavericks Calendar, replaced with a simpler, iOS 7-inspired theme. But the design improvements aren't the only new features coming to Calendar.
Calendar's new Maps support will help calculate travel times for appointments.
In addition, Calendar uses baked-in Maps support to help you figure out where you want to go (thanks to location suggestions), and travel-time calculations once you have an address in mind. Once you've selected a method of travel, the app will even bake that time into your appointment, and offer you the option to schedule a reminder for when you should leave the house.
OS X Mountain Lion was all about social interactions, building in support for Twitter, Facebook, YouTube, Vimeo, and Flickr. In OS X Mavericks, the social network gets professional: Yes, according to Apple's website, you'll soon be able to connect your LinkedIn account with your Mac--that is, assuming you still have a LinkedIn account.
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