Browser company Opera has launched a pre-alpha release of its Opera 10.5 browser and upgraded beta releases of its Opera Mobile 10 browser.

The company has released the browser for Labs, for Windows and Mac systems. A Unix and Linux version is due later. The release features the Carakan JavaScript engine.

"It's fast, more than seven times faster in [the SunSpider JavaScript benchmark] than Opera 10.10 with Futhark on Windows," said Roberto Mateu, product analyst at Opera, in a blog post.

Version 10.5 also features the Presto 2.5 rendering engine for handling HTML, CSS, and DOM. Improvements include support for CSS3 transitions and transforms, as well as more HTML 5 features such as persistent storage.

The Vega graphics library in Opera 10.5 displays what is seen on screen. It can be hardware-accelerated, although Mateu questioned whether hardware boosts would be needed.

There is no timetable for beta and general releases of Opera 10.5.

"Since this release is technically a 'pre-alpha' it's really just a preview of our long-awaited JavaScript engine, named Carakan, and our new rendering engine, Presto 2.5," said an Opera representativel.

Mateu cautioned that version 10.5 is still an unstable development build, with issues such as high memory usage. "There are known bugs, unimplemented UI elements, and surprise crashes," he said.

Users running the alpha release on Windows 7 or Vista will notice visual changes and the use of APIs allowing the UI to display the Aero Glass effect. For Mac, a rewrite in Cocoa brings a unified toolbar, native buttons and scrollbars, and multitouch gestures.

The alpha also features a Private tab or Private window that forgets everything that has happened once it is closed.

Downloads of Opera 10.5 can be accessed at the Opera Labs web page.

With upgraded beta versions of its Opera Mobile 10 browser this week, Opera is adding capabilities including faster loading, increased auto-rotation, and native keyboard input integration. Opera has positioned Mobile 10 as the browser bringing the desktop surfing experience to the small mobile screen.

Beta 2 for Windows Mobile touchscreen phones features faster loading; when the Opera icon is pressed, the browser will be loaded quicker. Additionally, auto-rotation now is supported on more phones.

The Windows Mobile beta also supports Hebrew and Arabic websites, with right-to-left rendering now working.

For Symbian/S60 phones, Opera Mobile 10 Beta 2 supports native keyboard input integration, with users able to use default keyboards to input characters and write in their native languages when, for example, they are searching Google or writing an e-mail.

Initial beta versions of Opera Mobile 10 were released in November. The second beta releases can be downloaded from Opera's web page.