ChartFactory is a free, open-source Java API for generating charts that can be saved as files or embedded in web or desktop applications. Unlike other API's, ChartFactory is extremely lightweight (the binary jar is around 32KB) and simple to use.
FLOSS study result by U of Maastricht and Berlecon Research
Transparent, multi-row bar chart
A line chart with a custom font and no point marks
Transparent pie chart
A bar chart with an embedded image and transparent bars