If you're a PHP developer and have recently switched to a Mac, you'll have noticed by now that setting up PHP and MySQL on Mac OS X (Apache is already bundled with Macs) is not that simple, especially for a newbie.
Luckily, MAMP (acronym for Mac, Apache, MySQL, PHP) comes to the rescue. This special-purposed application allows you to manage the three applications automatically on your Mac, making it ready to start coding your PHP-based web sites with MySQL databases right away.
The configuration created by MAMP is not intended to be the appropriate web environment for you to host your dynamic web pages, but at least is good enough for the developing stage. You can even choose between PHP4 or PHP5.
From: The Mac Newbie