jpcache is a lightweight, full page caching system for PHP which uses gzip content-encodig and ETag-headers. It allows around 80% in traffic-saving for php-pages and reducing server-load.
APC was conceived of to provide a way of boosting the performance of PHP on heavily loaded sites by providing a way for scripts to be cached in a compiled state, so that the overhead of parsing and compiling can be almost completely eliminated. There are commercial products which provide this functionality, but they are neither open-source nor free. Our goal was to level the playing field by providing an implementation that allows greater flexibility and is universally accessible. APC has been tested under PHP 4.0.3, 4.0.3pl1 and 4.0.4, and currently compiles under Linux and FreeBSD.
cgi_buffer is a group of libraries that may be used to improve performance of CGI scripts (and other content generation engines) in some circumstances, by applying performance-enhancing HTTP mechanisms that are typically not supported by them. Currently, Perl, Python and PHP are supported. The Python library may also be used as a wrapper around another CGI script.
The Zend Optimizer uses multi-pass code optimizations to double the running speed of PHP applications. This add-on is appropriate for all PHP users, who can benefit from the better response time featured by the product. The increase in speed for running PHP code reduces the CPU load for the server, and cuts in half latency time.