Due in the coming months for existing wp8 users. Shipping with the new lumias starting towards the end of the month
Pretty full overview
http://blogs.windows.com/windows_ph...eat-features-coming-in-windows-phone-8-1.aspx
Cortana
In Windows Phone 8.1, you get to Cortana by either a Live Tile on your Start screen or by pressing the search button on your device. This will take you to Cortana Home. To interact with Cortana, you can either speak or type—if you’re in a meeting, just type and Cortana won’t talk out loud. But if you ask her a spoken question, she’ll answer verbally and even carry on a natural conversation.
When you interact with Cortana for the VERY first time, she will start learning things about you... like your name, how to pronounce it, and ask for some personal interests.
Once she’s learned a bit about you, Cortana’s home populates with information that is curated just for you. You’ll see things like flight information she’s found from your email confirmations, weather, the latest news, and even traffic information once she learns your commute routine, such as from work and home.
Action Centre
Flow keyboard
The keyboard in Windows Phone is smart enough to learn your writing style and even knows the names of people in your contacts for faster typing. Best of all, our new Word Flow Keyboard lets you glide your fingers over the keys to type INCREDIBLY quickly… a kid was able to BREAK THE OFFICIAL WORLD RECORD previously held by the Swype keyboard on a Samsung Galaxy S4 using Word Flow by 8 seconds!
Lock screen themes
The Lock screen is the very first thing you – or your friends—see when you grab your phone, and in Windows Phone 8.1 we’re providing a new app that lets you set a wide range of interesting “Lock Screen Themes” which show all kinds of different visuals and animations. Make it yours…
start screen background and third column for all phones
In 2013, we added a third column on devices for 5-inch screen or larger devices, like the Lumia 1520, to enable more stuff to show up on the screen. People really liked this so we are enabling this on all screen sizes in Windows Phone 8.1. Pin away! We’ve also added the ability to customize your Start background with a favorite picture or one of the options we’ve provided, which will make many of the tiles on your Start screen become clear so you can see the background you selected as you scroll up and down.
new Skype app
The new Skype app for Windows Phone 8.1 brings the best of Skype on a smartphone. It’s integrated with the Phone dialer, so if you’re on a call you can quickly and easily “upgrade” your ordinary phone call to a Skype video call at the tap of a button! And… the new Skype app is designed to work seamlessly with Cortana so you can use Cortana to setup your calls within Skype.
new calendar
Separate slider for ring volume/media
we’ve improved the phone volume control by including separate sliders for your ringer/notifications and for your apps and media. Just the way you asked for it!
email supports S/MIME
Email now supports S/MIME secure email, and we’ve broadened our support for different account types, now including iCloud.
Business features
With Windows Phone 8.1, we’re making it even easier for IT professionals to manage devices and for professionals to connect to essential business apps and services with features such as customizable MDM enrollment, support for loads more MDM policies, LOB application & certificate management, S/MIME and VPN support. Stay tuned for a detailed blog post later today on the Windows for your Business Blog that covers all the key features for businesses.
combined app store with windows8.1update1
But only if developers update and allow it, they can still charge separately if they choose.
and some other stuff
Pretty full overview
http://blogs.windows.com/windows_ph...eat-features-coming-in-windows-phone-8-1.aspx
Cortana

In Windows Phone 8.1, you get to Cortana by either a Live Tile on your Start screen or by pressing the search button on your device. This will take you to Cortana Home. To interact with Cortana, you can either speak or type—if you’re in a meeting, just type and Cortana won’t talk out loud. But if you ask her a spoken question, she’ll answer verbally and even carry on a natural conversation.
When you interact with Cortana for the VERY first time, she will start learning things about you... like your name, how to pronounce it, and ask for some personal interests.
Once she’s learned a bit about you, Cortana’s home populates with information that is curated just for you. You’ll see things like flight information she’s found from your email confirmations, weather, the latest news, and even traffic information once she learns your commute routine, such as from work and home.
Action Centre

Flow keyboard
The keyboard in Windows Phone is smart enough to learn your writing style and even knows the names of people in your contacts for faster typing. Best of all, our new Word Flow Keyboard lets you glide your fingers over the keys to type INCREDIBLY quickly… a kid was able to BREAK THE OFFICIAL WORLD RECORD previously held by the Swype keyboard on a Samsung Galaxy S4 using Word Flow by 8 seconds!
Lock screen themes

The Lock screen is the very first thing you – or your friends—see when you grab your phone, and in Windows Phone 8.1 we’re providing a new app that lets you set a wide range of interesting “Lock Screen Themes” which show all kinds of different visuals and animations. Make it yours…
start screen background and third column for all phones

In 2013, we added a third column on devices for 5-inch screen or larger devices, like the Lumia 1520, to enable more stuff to show up on the screen. People really liked this so we are enabling this on all screen sizes in Windows Phone 8.1. Pin away! We’ve also added the ability to customize your Start background with a favorite picture or one of the options we’ve provided, which will make many of the tiles on your Start screen become clear so you can see the background you selected as you scroll up and down.
new Skype app
The new Skype app for Windows Phone 8.1 brings the best of Skype on a smartphone. It’s integrated with the Phone dialer, so if you’re on a call you can quickly and easily “upgrade” your ordinary phone call to a Skype video call at the tap of a button! And… the new Skype app is designed to work seamlessly with Cortana so you can use Cortana to setup your calls within Skype.
new calendar

Separate slider for ring volume/media
we’ve improved the phone volume control by including separate sliders for your ringer/notifications and for your apps and media. Just the way you asked for it!
email supports S/MIME
Email now supports S/MIME secure email, and we’ve broadened our support for different account types, now including iCloud.
Business features
With Windows Phone 8.1, we’re making it even easier for IT professionals to manage devices and for professionals to connect to essential business apps and services with features such as customizable MDM enrollment, support for loads more MDM policies, LOB application & certificate management, S/MIME and VPN support. Stay tuned for a detailed blog post later today on the Windows for your Business Blog that covers all the key features for businesses.
combined app store with windows8.1update1
But only if developers update and allow it, they can still charge separately if they choose.
and some other stuff
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