Let's collect all the new features in 8.1!

The purpose of this thread is to list all new features in Windows 8.1 (including ones that are confirmed but not available in the preview version yet).

Please add any additional features in the comment section (and, if necessary, add your source). I will update this post according to your contributions.

General

  • Boot to desktop option
  • Closing an app by dragging it down only removes it from the app switcher - the next time you open it, the app is restored immediately, as if you had not closed it. If you open the app immediately after closing it, it will restart from scratch with the splash screen. To fully shut down an app, drag it down and hold it at the bottom until the window turns into the app logo.
  • New cursor behaviour when using Modern UI by touch (select text by tapping on a word, move cursor by dragging it with your finger)
  • OS takes up less storage
  • Files stored on SD-card appear in apps
  • Switch between apps in pup-up media player controls
  • Touch cursor and marked text coloured according to the app's theme colour

Lock Screen

  • Slide show (local or SkyDrive pictures, optional seasonal slide show based on when the photos were taken)
  • Access camera by swiping down
  • Accept Skype calls from lock screen

Scaling

  • Scaling up to 200% for high res displays
  • Apps are rescaled automatically when dragged to another display with different resolution
  • Specific Start screen layout for portrait mode on small devices

Personalisation

  • Set background and accent colours separately
  • More colour nuances to choose from
  • Set desktop wallpaper as background for Start screen and apps list
  • New Start screen backgrounds (including animated ones, some of which move in sync with your scrolling)

Start Screen & Apps List

  • Large tile size
  • Small tile size (supports live information such as notification counts)
  • Coloured tile backgrounds for desktop apps
  • Rich tile designs enabled for desktop apps
  • Organize Live tiles and Start screen by pressing and holding (organize multiple tiles/apps at once)
  • Adjust scaling of the start screen
  • Number of rows of tiles not limited to 6
  • Access apps list by swiping up from the bottom of the Start screen (touch) of via down arrow button on the Start screen (mouse)
  • Option to go directly to apps list when you press/click Start
  • Sort apps list by name, date installed, usage or category (option to list desktop apps first)
  • New apps are not pinned to Start automatically (marked as "new" in apps list)
  • "Find app on Start screen" from apps list
  • Installation progress bar in apps list and on live tile

Hot Corners

  • Hovering Start "tip" replaced by Windows logo ("Start button")
  • Start button always visible on the taskbar (not optional)
  • Disable upper right and left hot corners
  • Charms icons are closer to the upper hot corner when user a mouse on a large screen
  • Shut down menu in "power user menu" (right click on start button or Win+X)
  • Command prompt replaced by Windows PowerShell in the power user menu (optional)

Multitasking

  • Up to 4 apps per display side by side (depending on screen resolution)
  • Multiple windows of the same app side by side (only with certain apps)
  • Resize windows to any size (minimum size equals snap view size in 8.0, apps automatically adjust content layout/view to size of window)
  • When an app is opened from another app, they are resized automatically and intelligently
  • No minimal screen resolution required
  • Drag windows across multiple displays
  • Indicators on the separation bars indicate, which of the windows you are actively using

Search & Share

  • Search Charm does universal search by default
  • Switch to contextual search via drop down menu (everywhere, settings, files, web images, web videos, current app), or use in-app search boxes
  • Universal search results shown directly opon entry (apps, settings, files, web search queries)
  • Play songs and videos from your library or Xbox collection directly from search results
  • Open URL with IE directly from search results
  • Hitting "enter" in universal search opens full screen results (behaves like an app), providing more or less rich results depending on the type of search query (including results from Bing websearch, Bing images, Bing videos, Wikipedia, local media files, Xbox music, biographical information, information related to places, related search terms)
  • Win+S shortcut for search charm from both Modern UI and desktop
  • Share content, screenshot or link to app in Store from any app

On-Sceen Keyboard

  • Swipe from a key in the direction of a pop up to type secondary characters (including numbers as secondary characters on the top row of keys)
  • 3 pop-up spelling suggestions below text, select by swiping across space bar
  • Autocorrect accuracy improved
  • 109 languages

Internet Explorer

  • Better performance
  • WebGL support
  • Option to always show address bar and tabs (no tabs preview image in this view)
  • Contextual menu for links and images is now in the app bar when using touch (press and hold)
  • "Hover" by touch (press and hold)
  • Multiple windows side by side (press and hold or right click IE tile on start screen, or press and hold a link or a tab to open it in a new window)
  • Tabs menu at the bottom above the address bar
  • Up to 100 tabs
  • Tabs synchronized across PCs
  • Restore multiple closed tabs (drop down menu in tabs menu)
  • Copy tab to open the same link in another tab (press and hold or right click a tab)
  • Multiple web search suggestions appear next to suggested links as you type in address bar
  • Certain information (such as weather) shown directly above address bar as you type
  • Search or share selected text via contextual menu (press and hold or right click)
  • Add bookmark to reading list (share charm)
  • Phone number detection for Skype
  • Live tiles showing RSS feeds for pinned websites (website needs to have live tile support build in, see http://www.buildmypinnedsite.com/, example for website with live tile support: http://www.blogs.windows.com/)
  • Select image from website as tile image when pinning a website to the start screen
  • Subfolders for favorites
  • Manage accounts and passwords (settings charm)
  • View and manage downloads (via tools menu in app bar)
  • The Verge forum post editor supported ;)
  • Reading view (not available in preview)
  • "Swipe ahead to next page" in desktop version as well

Store

  • Apps presented with description and rating instead of tiles
  • Home page with featured apps, picks for you, popular now and new releases
  • App bar with links to home, your apps, your account and categories
  • Recommendations ("picks for you") based on installed apps, app rating, region and other factors
  • Browse similar apps and other apps by same developer from app page

SkyDrive App

  • Doubles as local file manager
  • Faster
  • Upload local folders and files to SkyDrive via app bar
  • Photos app integrated into Skydrive app (edit photos from within Skydrive app)

Mail (not in preview)

  • Filter for social network notification mails, newsletters, mails by favorite people
  • Delete multiple mails of a certain type at once
  • Drage & drop

Music App

  • Navigation menu: collection, radio, explore, playlists
  • Import playlists (including playlists from iTunes)
  • Create playlist from website containing information on artists/albums/songs via share charm (not available in preview)

Photos App

  • New design and navigation (only local library accessible in preview)
  • Advanced editing tools (preset filters, remove red eyes, retouching, brightness, contrast, highlists, shadows, temperature, tint, saturation, colour enhance, vignette, selective focus)

Camera

  • Photosynth (full panorama) built in (view panoramas "augmented reality" style using motion sensors)
  • Adjust brightness

Reader

  • View multiple files in tabs or multiple windows

Other preinstalled apps

  • "Substantial updates" to all preinstalled apps (not all available in preview)

New Apps

  • Outlook RT (desktop version, lacks some advanced features, preinstalled on Windows RT)
  • Reading List (save links or app content for later via share charm, synchronised across PCs)
  • Bing Food & Drink (find recipes from online sources and a selection of chefs, plan meals, create shopping lists, learn cooking skills, hands-free flipping through recipe pages by waving hand in front of webcam)
  • Bing Health & Fitness (monitor nutrition habits, exercise routine, overall health; get diagnoses by entering symptoms)
  • Alarm (alarm, stopwatch, countdown timer)
  • Calculator (numeric, scientific, unit conversions)
  • Scan
  • Sound recorder
  • Help & Tips (on how to use Windows 8)

PC Settings

  • Most settings accessible in Modern style PC settings app (as well as the traditional Control Panel)

SkyDrive Integration

  • Fully integrated into file system (file system devided into "SkyDrive" and "This PC")
  • File information and previews automatically synchronised
  • Select files, folder, or all content to be synchronised for offline access
  • PC settings, app settings and app data synchronised across multiple PCs
  • Manage SkyDrive storage via PC settings

Networking, Businesses, Security

  • Miracast support (wireless screencasting)
  • WiFi direct printing supported (driverless printing with compatible printers)
  • NFC tap-to-pair printing
  • 3D printing support (print via devices charm)
  • Broadband tethering (use device with 3G/LTE as a hotspot)
  • Enterprise features (temporary access to cntent controlled by IT department, Workplace Join to control access to data, auto-triggered VPN to sign in to intranet sites, Work Folders = SkyDrive for enterprises, Open MDM built into OS, IT departments can control Start screen layout and installed apps on devices brought by employees)
  • Assigned Access (formerly known as "kiosk mode")
  • Windows Embedded 8.1 Industry
  • Network Behaviour Monitoring in Windows Defender
  • Fingerprint authentification support (for logging in to user account, accessing folders, purchasing apps, logging in to apps, purchasing from within apps)
  • Virtual Smart Cards support