If you need to create charts or other sorts of plots for a website, it can be a difficult problem. Many web scripting languages like PHP have the underlying functionality, in the form of the GD library, to tackle this problem. But it's a lot of work to build up your own charts and graphics from scratch using GD.

If you're using PHP, check out pChart. It takes care of all the behind-the-scenes nightmares and makes it really easy to create your own images dynamically in PHP. It can handle many types of lines charts in additions to creating pie charts (for the sales and marketing folks).