Open Flash Chart is a great opensource chart plotting framework.  It uses pre-compiled Flex objects to display data.  JSON formatted data is sent to the OpenFlashChart SWF file to produce all sorts of graphs (ie: area, vertical and horizontal bar, candle, line, pie and radar graphs).  It is fairly easy to customize and implement.

Here is a brief work-flow when using OpenFlashChart.  Look at the resource links at the bottom of this post for a more detailed explanation and more examples.

JSON formatted data is fed directly into the OpenFlashChart SWF file, which parses the data and plots it on the desired graph.  The JSON data can be stored in a text file or can be created dynamically using PHP and the OpenFlashChart PHP library.  You will have to look at the library to see all the options for formatting the data properly, but here is a quick example:

include ‘php-ofc-library/open-flash-chart.php’;

$bar = new bar();
$bar->set_values( array(1,2,3,4,5,6,7,8,9,10) );

$chart = new open_flash_chart();
$title = new title(‘My First Graph’);
$chart->set_title($title);
$chart->add_element($bar);

$chart->toPrettyString();

We can also write the JSON data into a JavaScript variable to create a chart for use in AJAX.  OpenFlashChart also comes with libraries other than PHP, such as .NET, Perl, Python, Ruby, JavaScript and Java with Google Web Tools.

Here are some examples of the graphs produced with OpenFlashChart:

Useful Resources:

Open Flash Chart

http://teethgrinder.co.uk/open-flash-chart/

Open Flash Chart 2

http://teethgrinder.co.uk/open-flash-chart-2/

Open Flash Chart Extended

http://code.google.com/p/ofcgwt/

http://code.google.com/p/ext-ux-ofcgxt/

Tutorials

http://teethgrinder.co.uk/open-flash-chart-2/tutorial.php