Imbalance is a lightweight redirector that runs as an Apache PHP Script, a PHP based daemon which uses MySQL to maintain persistent state across booting of the host system. Imbalance uses a cost based round-robin weighted algorithm.   Code: PHP 4.0

Turck MMCache is a free open source PHP accelerator, optimizer, encoder and dynamic content cache for PHP. It increases performance of PHP scripts by caching them in compiled state. Typically reduces server load and inreases speed of PHP code 1-10 times.   Code: PHP 4.0

RFKcache is an easy and efficient cache engine for PHP programs. RFKcache can be used to optimize a variety of PHP programs by providing cached code to decrease load times and inrease overall performance.   Code: PHP 4.0

This class caches output generated by your PHP files and uses the cached version, instead of generating the content again and again, until cache file expires after a specified amount of time, thus, greatly improving the speed of your websites.   Code: PHP 4.0