Allan MacGregor has a post today talking about a handy tool he uses in his development to have multiple versions of PHP running side-by-side: PHPFarm.

If you have been working with PHP for a while, chances are that you have come across with a project, extension or script that requires to be tested on multiple PHP versions, for simple CLI scripts this seems easy enough but what happens when you are working with complex applications, developing for frameworks or multiple versions of them? [...] This setup can quickly become cumbersome and it is not easily scalable. [...] Getting multiple PHP versions running side by side can be challenging and over the year devs have released multiple solutions like PHPEnv or the new , personally I use PHPFarm.

He walks you through the installation and configuration of the tool. He also shows you how to get a few different versions of PHP installed, including custom configuration files. He also includes a bit at the end of the post about getting it all to work with Apache (via mod_fastcgi and some custom configuration changes).