As is mentioned in this new post to PHP.net today, they've released the latest alpha for the PHP 5.5.x series - PHP 5.5.0alpha6 - for testing. This is not a stable release so do not use it in production by any means.

The PHP development team announces the release of PHP 5.5.0alpha6. This release fixes some bugs from alpha5. It also serves as a delay for our next release, beta1, integrating ZendOptimizer+ OPCode cache which is not ready yet to be merged. All users of PHP are encouraged to test this version carefully, and report any bugs in the bug tracking system.

Updates in this release include a fix for a bug where uninitialized ++$foo->bar; does not cause a notice, an update to the bundled PCRE 8.32, and a bugfix in ext/sockets where sendmsg/recvmsg shutdown handler causes segfault. You can get the complete list of changes here and get the download over on this site (Windows users here).