We were recently tasked with the redesign of a fairly large intranet application which used Microsoft Active Directory for user authentication. The previous version of the site was created with ASP/VBScript and so our first challenge was duplicating (or in this case, improving) the LDAP connection system using PHP.
The vast majority of PHP sites are built using a LAMP setup. For the uninitiated, this indicates a server running a Linux operating system, Apache web server software, a MySQL database, and the PHP development language. There are several reasons why this set of software is so popular, but the key ones are cost (free), security, reliability, and a wide open-source development community. However, in a recent custom project we were tasked with setting up a new intranet site which was effectively married to a Windows/IIS server running MS SQL.
We launched a rather large e-commerce site recently, and one of their requirements included a report that allowed administrators to mark purchases as processed -- the client had a much larger donor management system that was separate from the website's database and needed to make sure that orders were recorded in the other system.