XCache is a open-source opcode cacher, which means that it accelerates the performance of PHP on servers. It optimizes performance by removing the compilation time of PHP scripts by caching the compiled state of PHP scripts into RAM.
The Alternative PHP Cache (APC) is a free and open opcode cache for PHP. Its goal is to provide a free, open and robust framework for caching and optimizing PHP intermediate code.
An easily installed PHP Zend engine extension that provides a PHP cache, and is capable of delivering a substantial acceleration of PHP scripts without requiring any script changes, loss of dynamic content, or other application compromises.