The implementation of fastcgi for php is called php-fpm where FPM stands for FastCGI Process Manager.
fastcgi spawns a number of worker processes that wait for requests. It increases performance by not re-initializing the PHP engine on each invocation, allowing each process to deal with a number of requests before it recycles.
FPM is an alternative PHP FastCGI implementation with some additional features (mostly) useful for heavy-loaded sites.
php-fpm was previously found at http://php-fpm.org
but starting from release 5.3.3 in early 2010, PHP has merged the php-fpm fastCGI process manager into its codebase, and it is now (as of 5.4.1) quite stable.
From release 5.3.3 onwards, PHP now includes the fastCGI process manager (php-fpm) in the stock source code.