Presto 2.5
Presto 2.5 includes several new features like CSS transformations, HTML5 local storage (and soon video). But most important of all, support for Carakan. Carakan is the new JavaScript engine that is completely written from scratch. Using a JIT compiler it is many times faster than Futhark, the javascript engine in 10.10.
Operas caching system has also undergone a major rewrite. A nice feature in the new cache system is opera:cache, which allows you to browse through everything that Opera has stored on memory or disk. But the new cache system is most importantly much faster. You should definitely notice shorter startup and shutdown times. M2 users with a lot of mail will in addition benefit from the mail database reading optimizations that have been done to speed up startup.
Another big technological change is happening in graphics rendering. In Opera 10.10, VEGA (Opera's vector graphics library) is only used for rendering SVG. In Opera 10.5 VEGA is used for rendering all graphics in Opera, including content on webpages and the user interface. Currently VEGA is a pure software rendering engine, with the possibility to add hardware accelerated back-ends in future releases. But the software rendering is incredibly optimized, which means that Opera 10.5 has very fast painting performance even without using hardware acceleration.

Platform Integration

If you're using Mac OS, you will notice that Opera looks a lot more Mac-ish. This is the result of some big changes under the hood. Opera 10.5 for Mac has moved to using the Cocoa framework, which makes it possible to introduce the Unified Toolbar, more native user interface widgets and support for Growl. Note that not all functionality has been ported to Cocoa yet, so some features (like printing) won't work and the performance isn't optimal yet.
Windows users will see some major visual updates too. Aero Glass support makes Opera 10.5 look nicely integrated on Windows 7 and Vista. And off course 10.5 support Jumplists and Aero Peek. To maximize the space available for webpages Opera does not show the menu bar by default anymore. All the menus are still accessible trough the Opera button

New and improved features
If you share a computer with other people, you might be interested in Private Mode. Contrary to other browsers, Opera make it possible to have both Private Windows and Private Tabs. You can also quickly close all private tabs and windows with a shortcut.


One of the biggest usability improvements in Opera 10 is the handling of dialogs. Most interactive dialogs will no longer block tabs or disturb your work flow. Tab specific dialogs (like javascript popups) are displayed as part of the tab in an overlay, so you can easily switch tabs without have to move or close the dialogs. Other dialogs, like find in page, are now displayed as toolbars on top of the webpage so they don't overlap the webpage anymore. Find in page also has improved highlighting of search results and finds results as you type.






No Unix … yet!
Don't worry, Unix users will not be forgotten. Like Opera for Mac, the Unix version will have some big changes under the platform hood: it will no longer be necessary to have Qt installed. This makes Opera for Unix much faster, smaller and easier to install. Naturally Opera will still integrate well with your desktop environment by supporting KDE/GTK skinning and show open/save dialogs that match your desktop. The Unix version of this labs release will be made available later.

10.2 and widgets
In 10.2 alpha we showed the next generation of our Widget implementation. This will soon be part of Opera 10.5 too. And with full focus on 10.5, there will not be new releases of 10.2.

Warning
This build is pre-alpha quality. It's intended as an early showcase for new technologies. It might freeze your computer, corrupt your data, embarrass you in front of your friends or worse. Don't upgrade your existing Opera installation with it.
Known issues: JIT doesn't work on CPU's without SSE2, printing and PowerPC are not supported on Mac, Memory usage can be high, Opera will regularly quit unexpectedly. Some features, like Opera Unite are disabled.

Download the build from Opera Labs