New features

Better integration with the Windows operating system

• Windows 7:
  • Aero Glass
  • Aero Peek
  • Jump Lists

Opera Carakan JavaScript engine

• Cross-platform bytecode interpreter for a new register-based instruction set
• Internal object model with automatic classification and inline property caching
• Machine code generation (JIT compiler)
• Divided garbage collection heap: automatically traverses the memory of active heaps
• Caching of compiled programs
• Reduced memory usage
• Additional Carakan information (http://my.opera.com/core/blog/2009/12/22/carakan-revisited)

Opera "O" tab and menu
The new Opera "O" tab and its associated menu (located on the left side of the Opera Tab bar) replaces the traditional Opera Menu bar. This increases vertical space in the Opera desktop window, and centralizes frequently used features and tools in one, convenient location. Optionally, the new Opera "O" tab and menu can be replaced with the traditional Opera Menu bar by clicking "Show Menu Bar" in the Opera "O" menu. This new Opera feature contains the following items.

• Tabs and Windows ?
• Page ?
• Print ?
• Bookmarks ?
• History
• Downloads
• Opera Unite ?
• Synchronize Opera ?
• Widgets ?
• Notes
• Mail and Chat Accounts
• Mail ?
• Contacts
• Appearance
• Settings ?
• Help ?
• Show Menu Bar
• Exit

Opera Presto 2.5 rendering engine
The beta 2 release of Opera 10.50 (with Opera Widgets for Desktop) for Windows contains the latest Opera rendering engine: Opera Presto 2.5, and employs the following features from it.
CSS

• CSS 2.1 visibility: collapse
• CSS3 border-radius property (rounded corners)
• CSS3 Backgrounds and Borders
• CSS3 2D Transforms
• CSS3 Transitions

HTML5

• HTML5
• HTML5 element (child of the HTML5