On PHP.net today they've announced the release of the latest Release Candidate in the PHP 5.5.x series - PHP 5.5.0RC2.

The PHP development team announces the availability of the second release candidate of PHP 5.5. This release fixes some bugs against RC1 and improves overall stability. [...] Please help us to identify bugs in order to ensure that the release is solid and all things behave as expected. Please test this release candidate against your code base and report any problems that you encounter to the QA mailing list and/or the PHP bug tracker.

Issues corrected include a segfault when memory was used up, an issue with mbstring in PHPT tests in Windows x64 and a problem with custom exceptions. You can find the full list of changes in the NEWS file. Please download this latest release candidate (Windows here) and test it out on your systems.