What's new in Windows Phone 8.1

Applications

Removed Facebook integration on ">" screen
Also on the screen of ">Is it because of how bad the app has always been?
"Redesigned the Games screen. Until we have a sample of the new design, little more than to applaud a good facelift of this green screen. And that the avatars of our friends are even more alive ."
Music and Video will be independent applications instead of the current Music + Video screen (allowing more updates via push ) Another good decision, because the use of both they have nothing to do from the point of view of the user experience."
Updated camera layout, similar to Windows 8.1, including burst mode. So I can specify the capture period for burst photos so they don't fill up the phone.Obviously there must be news that new players/manufacturers arrive on the market, because it is direct competition to Nokia and a nod to the rest of the device manufacturers.OneDrive (formerly SkyDrive) arrives with built-in file browser (just like Windows 8.1). Another one at last!! That the integration of SkyDrive was rather bad in Windows Phone, and it becomes more and more necessary. And more with the phablet just around the corner.
Internet Explorer 11 has been enhanced with WebGL and support for Normal mapping (a way of texturing objects). The tabs button has been removed and multitasking view becomes the primary way to view tabs.
Password, tab, history and bookmark manager sync with IE desktop.
IE has the ability to upload and download files. Downloads are stored in the downloads folder, and can be shared between applications and NFC.
IE has a reading mode and InPrivate browsing mode. Wow, looks like we're going to have an Internet Explorer to match any Windows 8 Special note synchronization of all browsers on any Windows device, and browsing InPrivate (no, it's not only for porn) very useful for banking from your mobile.
"Unlike Facebook, Twitter is more deeply integrated into the Contacts screen."
New possibility to select your own default messaging application
New Podcast app. Another application that all users have been waiting for and that balances forces with iOS and its excellent iTunes to listen to these audio programs.
Removed the ability to post to various social networks. Instead it's going to make it work more like sharing works in Windows 8, where we're presented with a list of apps I can share the content with.
The Calendar app has a new weekly view.
Bing apps via phone and PC will sync with each other using Windows Account.
You can configure the contact list to show only those who have a phone number.
Email: Can be set to always download images attached to emails. Encrypted and signed email support. New email synchronization options, based on usage patterns (for example, if a lot of email is retrieved on certain days and I don't want to check my mailbox every day).
"Office photo app (Windows Phone lens concept). It will allow you to scan whiteboards and documents directly into the camera, optimizing images to be clear and easy to read in My Notes."
Support Office documents protected by password.
The wallet may support Tickets and membership cards.
The Close Circle of contacts could support up to 40 contacts. In summary, a very powerful update of the capabilities of the different applications included in the operating system. Some very important, some almost anecdotal, but all very useful. And many of them indicate the path to unification with Windows 8 seeking the paradigm that the device where the application runs does not matter, that the user experience is always the same.

Search and new services

Single sign-on for apps (like in Windows 8) with Microsoft Accounts, you'll stay signed in across all devices and apps with permission. Once again, the unification of the ecosystem is seen everywhere.With this I will be able to stay validated in an app, regardless of the device I am using on each occasion.
Cortana personal assistant that uses Bing services and FourSquare data sets. It's much better now to understand the injection of millions that Microsoft just made into FourSquare, and the image of Cortana emerging from my smartphone sends shivers of delight through my spine. We are all going to feel a bit like the Master Chief.
Bing Smart Search (similar to Windows 8.1 system). And that outside the USA, it will continue to be much lower than the results of Google. Let's see if they open their hand once and allow them to implement the quality and quantity of information that is obtained in Bing USA.
iCloud Support. WTF?
Windows Store will recommend apps based on location and recommendations from my friends on Facebook. One more step so that everything and everyone is connected in the Internet of Things... or in Skynet .
Settings to mute a messaging conversation. Of all the new features, what stands out to me the most is the iCloud support and the expectation to see how Cortana is implemented, and that it is nothing like the Office assistant.

Compatibility

New apps for Windows Phone 8.1 will not work on Windows Phone 8.
All current Windows Phone 8 phones and devices can be upgraded to Windows Phone 8.1 A huge sigh of relief as I read the second line. But don't forget that this is the end of everything for 7.1 devices Because development companies are not going to make a 7.x app when they are forced to to migrate the entire park of applications to 8.1.

Now we have to see if App 8.0 will work in 8.1.

Navigation and interface

I can close apps by swiping down, Windows 8 Modern UI style.
I can pick and choose the color of the Navigation Bar.
The Back button does not end the application, but rather suspends it. I suppose it will be with the objective of eto avoid those inopportune exits of the applications for having pressed the back arrow too many times.
More efficient multitasking. I don't know if you mean faster, less battery or memory consumption. But right now it's pretty good.
Be able to filter the list of applications installed by use / installation date.
Access to quick settings (Wi-Fi, Bluetooth, etc), performing a quick swipe from the top of the screen. Also very Windows 8, and it reminds me a lot of the excellent Android system.
Accessing the Notification Center is accessed by swiping the entire screen from top to bottom.
Ability of applications to manage notifications. Being able to delete them, update them, etc.
RUMOR: New large Tile.
RUMOR: Mark a Live Tile as read, swiping from the left edge of the tile itself.