The central power of PHP is it’s free simple,light weight and faster than other server side programming languages. PHP is influenced by C,C++,Perl,Shell programming of LINUX and many more. Some killer application such as Facebook,funnonsms and lot of light weight website developed by PHP you may find in www.
Some version of PHP ,are
PHP3 in 1997
PHP4 in 1998
PHP5 in 2004 (With object oriented feature and fit for scalable application)
and new version is knocking at the door of programming languages.