All of this discussion takes me back to a project I did a couple of years ago. I wrote a booking and scheduling system than ran (and as far as I know still does) a big TV screen in the middle of Manchester. I consisted of a WAMP (Windows, Apache, MySQL, PHP) server which we built that talked to our proprietry broadcast control system. The users created/edited bookings via a web interface which then told our control system to route sources to the screen, control DVD players, switch GPIO's etc.

The bit that got us all confused was because the Apache, MySQL and PHP where all licensed open source and free to obtain, where did we stand with charging them for it all.

I don't think lawyers were ever consulted, but basically I think we charged them for our proprietry software, the cost of the hardware and the effort involved of writing the PHP scripts and configuring web server. As far as anyone was concerned the customer downloaded the 'AMP' portion themselves.

To this day I'm unsure as to how legal this whole situation was and I'd be interested to know.