Cucumber is a Behavioural Driven Development framework written in Ruby. Using a wire it allows to write BDD steps in PHP to test PHP applications. Cuke4php is in fact a wire protocol implementation of Cucumber written in PHP.

You'll still need to have Cucumber (Ruby) installed on your testing system, but pulling in the Cuke4PHP tool is as easy as pointing your "pear" command-line tool at their PEAR server and installing. With a little bit of configuration (and possibly an install of PHPUnit) you'll be up and running. You can then write Cucumber tests that can run against your PHP code. They've included a sample PHP class and a Cucumber test to match it.

Unlike any other PHP testing framework that tests applications inside out. Behat is testing applications outside in. It means, that Behat works only with your application's input/output. There are Symfony plugin and Symfony2 bundle for Behat, so you can start testing your applications right now.

Behat is an open source behavior-driven development framework that's PHP 5.3 only inspired by Ruby's Cucumber project. You can install it in one of two ways - either from their custom PEAR channel (pear.everzet.com) or by cloning their github repository. The Behat site has some example tests to get you started.