Smarty is a PHP template engine written by Monte Ohrt and Andrei Zmievski. Yet another template engine you say? The authors (and I too) would disagree. Smarty is different from the rest of the pack. What differentiates Smarty from other template engines like FastTemplate and patTemplate is that Smarty compiles your templates into PHP scripts, eliminating the overhead incurred in parsing the templates every time they're accessed. This makes Smarty very scalable for large applications and high-traffic Websites ...and if that didn't make any sense to you, just take it that Smarty is very fast and would work well in stressful and high-traffic conditions!
The Smarty template engine has several other outstanding features besides template compilation, read the complete article by By Cheah Chu Yeow at http://www.sitepoint.com/article/smarty-php-template-engine