Among the many improvements to PHP 5.4 is support for language traits, a shortened array syntax, a built-in web-server, compatibility changes, and many other improvements.
Besides the language changes for PHP 5.4, a built-in web-server for this scripting language is also quite interesting as it no longer means needing a web-server like Apache/HTTPD or NGINX in order to test simple web applications. At this point the built-in PHP web-server, which can be easily started from the command-line, is just intended for testing/debugging purposes. However, coming up for Phoronix Test Suite 4.x later in the year I do have some nifty features in-development that's built around the support.
For more details on the PHP 5.4.0 release, see the release page and the migration guide.