If you'd like to help with testing for the upcoming PHP 5.5.0 version, they've announced the release of the latest alpha on the PHP.net site, ready for download and test execution.

The PHP development team announces the immediate availability of PHP 5.5.0alpha2. This release adds new features and fix some bugs from alpha1. All users of PHP are encouraged to test this version carefully, and report any bugs in the bug tracking system.

You can see the full list of the changes in 5.5.0 (so far) in the NEWS file including things like using empty on return values, enabling systemtap by default for dtrace probes and optimized variable accessing. They need your help to make this upcoming release even better, so if you'd like to help out and test, go grab the download (Windows builds).