The PHP development team is proud to announce the second beta release of PHP 5.4. PHP 5.4 includes new language features and removes several legacy (deprecated) behaviours. Windows binaries can be downloaded from the Windows QA site. [...] Please help us to identify bugs by testing new features and looking for unintended backward compatibility breaks, so we can fix the problems and fully document intended changes before PHP 5.4.0 is released. Report findings to the QA mailing list and/or the PHP bug tracker.
Remember - this is not a production release, so do not use it in your live applications (unless you really like to live dangerously, of course). You can look at the NEWS file for a complete list of changes.