This is item 4 so far in my list of open source/freeware/shareware/beta software. And this is by far one of my facroite pieces of software on my machine. I have been using this for a while now (a year or so) and it has aided me so much.
Basically WAMP is Windows/Apache/MySQL/PHP and installing it will run a server capable of handling each protocol on your PC. This makes life SOOOO much easier if you are trying to learn PHP/MySQL or if you are working on a program and need a stable constant enviroment to test it in.
For example, I am working on a browser based game using PHP/MySQL and I am using my personal PC as the testing grounds for it until I am ready to launch it. I am able to build all the PHP pages, test them, edit and watch them work all on my home machine and I am also build all my databases access them and view the data just as easily. This is much easier than trying to use a FTP to someone elses server.
Plus, using WAMP to install all these services is a breeze. Everything is already set up for you. All you need to do it set the default ports and the directory adn your good to go. Everything is already set up to work with each other.
All the services are the newest stable version and basically as soon as one is updated, WAMP is update and available. Its a great crew that created and maintains it.
Personally one of my FAVORITE pieces of open source software out there!