The first Release Candidate of PHP 5 is finally here! The move from Beta stage to RC stage means that PHP 5 is now feature complete, and is quite stable - stable enough for everyone to start playing with. Note that it is still not recommended for mission-critical use.
Some of the key features of PHP 5 include:
The Zend Engine II with a new object model and dozens of new features.
XML support has been completely redone in PHP 5, all extensions are now focused around the excellent libxml2 library (http://www.xmlsoft.org/).
A new MySQL extension named MySQLi for developers using MySQL 4.1 and later. Additionally to a functional interface this new extension also includes an object-oriented interfaced and support for many of MySQL's new features such as prepared statements.
SQLite has been bundled with PHP. For more information on SQLite, please visit their website.
A brand new built-in SOAP extension for interoperability with Web Services.
A new SimpleXML extension for easily accessing and manipulating XML as PHP objects. It can also interface with the DOM extension and vice-versa.
Streams have been greatly improved, including the ability to access low-level socket operations on streams.
And lots more...
For changes since Beta 4, please consult the ChangeLog
News source: PHP.NET