Chris Jones has a new post to his Oracle blog today talking about the new "opcode" opcode caching that's going to be built into future PHP versions This is the implementation of the Zend Optimizer+ opcode caching in a native language interface. The latest PHP 5.5 snapshots have it included.
The new "opcache" can be seen as substitute for the venerable APC cache, the maintenance of which had become an issue. Note: although opcache is now readily available, there is currently nothing preventing you from using any available (working!) opcode cache in PHP 5.5.
He gives you a quick guide to getting this new opcode caching enabled and compiled into a shiny new download of the PHP 5.5.x branch. You'll need a special command line flag on the compile and to update your php.ini to load the needed shares module. You can also use it if you're on PHP 5.2 or higher either by compiling this source or using this PECL extension.