From the press release:
Zend Technologies, Inc., the PHP Company, today announced that it is offering a free developer's version of Zend Platform, its PHP runtime optimization technology, to all buyers of Zend Studio Professional 5.2, the industry leading software development environment for PHP.
Zend Platform enhances PHP deployments with real-time debugging, monitoring, configuration, performance management, clustering, and Java integration. The functionality of the developer's version is identical to the production version of Zend Platform, enabling PHP developers to get their applications to deployment faster and reducing the frequency and severity of post-deployment problems in their PHP applications.
To grab your free developer's copy of the Zend Platform software, head over to this page on the Zend site and click on the "Download the Zend Platform Trial and request a Developers License" link.