PHP 5 features the Zend Engine 2. For a list of Zend Engine 2 changes, please <a href="http://www.php.net/zend-engine-2.php"target="_blank">visit this webpage;
XML support has been completely redone in PHP 5, all extensions are now focused around the <a href="http://www.xmlsoft.org/"target="_blank"> excellent libxml2 library (see xmlsoft.org);
SQLite has been bundled with PHP. For more information on <a href="http://www.hwaci.com/sw/sqlite/"target="_blank"> SQLite, please visit their website. ;
Streams have been greatly improved, including the ability to access low-level socket operations on streams. For every PostNuker who wants to play with the newest version!