New tricks to an old dog
Some time ago I developed a small project that put together a few software pieces to create a monitoring system. I've used for development a great graphics library built in PHP called JpGraph. It did the work but I realized that the software license required payment of $600 for each website that use it commercially.
As my system was like an Internet appliance and each customer had a different unit (and address) it seemed that I would need to add $600 to the price tag of the system to be compliant with JpGraph license. It was time to look for an alternative, as there was no way the product price could support that extra cost. So I found libchart library that worked nicely with PHP5 (provided you already have GD support built-in).
The end result looks ok too, though libchart lacks many of the features of JpGraph, it is still good enough for my application. Libchart author licenses the software with GPL3 and while the software is free, he's accepting donations.