Opera Software has quietly announced the release of Opera 7.50 Preview 3, the first release of the Web browser for the Mac using Opera’s 7.x codebase. The completely says that the software is nearly a complete code rewrite and sports Opera 7’s Presto rendering engine. Other features include Opera Mail, Opera Chat, integration with Keychain, and more. A detailed list of changes is available here. “This release is unfinished and unsupported beta-quality software,” notes Opera. “It cannot be registered, but will not expire. This release requires Mac OS X 10.1 or later. We recommend always using the latest operating system updates. Please use the latest release of Macromedia Flash.”