php.net:

The PHP development team is proud to announce the first alpha release (Windows binaries will appear in the next few days) of the upcoming minor version update of PHP. The new version PHP 5.3 is expected to improve stability and performance as well as add new language syntax and extensions. Several new features have already been documented in the official documentation, others are listed on the wiki in preparation of getting documented. Please also review the NEWS file.THIS IS A DEVELEOPMENT PREVIEW - DO NOT USE IT IN PRODUCTION!The purpose of this alpha release is to encourage end users to noy only actively participate in identifying bugs, but also in ensuring that all new features or necessary backwards compatibility breaks are noted in the documentation. Please report any findings to the QA mailinglist or the bug tracker.There have been a great number of other additions and improvements, but here is a short overview of the most important user visible changes:Namespaces (documentation maybe out dated)Late static binding and __callStaticLambda functions and closuresAddition of the intl, phar (phar is scheduled for some more work a head of alpha2), fileinfo and sqlite3 extensionsOptional cyclic garbage collectionOptional support for the MySQLnd replacement driver for libmysqlWindows older than Windows 2000 (Windows 98, NT4, etc.) are not supported anymore (details)New syntax features like NOWDOC, limited GOTO, short "?:" ternary syntaxSeveral under the hood changes also require in depth testing with existing applications to ensure that any backwards compatibility breaks are minimized. This is especially important for users that require the undocumented Zend engine multibyte support.The current release plan states that there will be alpha/beta/RC releases in 2-3 week intervals with an expected stable release of PHP 5.3 between mid September and mid October of 2008.