Features
- Added support for Linux
- Offline messaging: You can now send messages to users who are offline. They will receive the message when they next log in
- Opening a chat dialog with a friend will show some recent chat history
- A web chat interface is available, you can find it by navigating to the Steam Community Friend Activity page in your web browser
- Added a caps lock warning indicator to the login dialog password textbox
- Added support for better content sharing between games
- Improved performance and responsiveness of client UI
- Improved startup time for users with large screenshot folders
- Prevent users from selecting an invalid screenshots folder
- Suspend all downloads automatically when a game is launched
- Added third party Mod support for games on new content system
- Big Picture: Users can now add wallet funds and authorize microtransactions
- Big Picture: In-game overlay now moves back on ESC when appropriate rather than closing directly
- Added the date that SteamGuard was enabled in the settings dialog
- Improved handling of international characters

Fixes
- Fixed several issues with scroll bars in the store and community views
- Fixed forum links opening in external browser windows
- Reduced retail install time when reading from optical disc on Windows XP/Vista
- Removed "/me" chat command, which allowed some users to modify the color of their chat text
- Fixed crash on startup caused by corrupt ClientRegistry.blob file
- Fixed a top crash related to video streaming
- Fixed an issue with cascading menu items
- Fixed issue where some game installers cannot write to the registry
- Fixed screenshots sometimes not showing up in screenshot manager when copied from another Steam installation
- Big Picture: Fixed left/right navigation of game related sections in the in-game overlay
- Big Picture: Fixed default font used by the in-game overlay
- Fixed launching 64-bit games and applications
- When a friend's status changes multiple times consecutively, only the last change will be shown (ie "Friend is now Online", "Friend is now Away" messages)
- Fixed Windows error message "Disk not ready" in game install wizard
- Made the preview image for guides smaller in the overlay
- Caching guide preview images when viewed in the overlay
- Added Ctrl+A select-all for system info text

Mac
- Greatly reduced CPU usage and power consumption
- Fixed command-W and other keyboard shortcuts
- Fixed bugs with window management and the Window menu
- Fixed leaks which caused memory usage to increase over time
- Added partial support for Retina displays
- Fixed bug with tooltips showing through Windows
- Notification popups now respond on the first click
- Web page views no longer freeze up after clicking and dragging the mouse
- Clicking the dock icon now brings all Steam windows to the front