The Zend Optimizer is a free application that runs the files encoded by the Zend Guard, while enhancing the performance of PHP applications.
For enterprise-class performance enhancement with an up to x25 increase in server throughput, try Zend Platform. Zend Platform's Performance Enhancement Technology was specifically created to help optimize the responsiveness and processing efficiency of robust, high traffic PHP-based sites. At the same time, Zend Platform's PHP Intelligence Module provides insight into performance bottlenecks and run-time errors.
For PHP versions below 4.0.4, use the Zend Optimizer 1.2.0.