Mature JVM library for generating charts and graphs in various formats (PNG, SVG, PDF, and more). Used in Charles Nutter's JRuby blog post as an example of pulling a JVM library into JRuby via a `jar-file` declaration and `lock_jars` (analogous to Gemfile + bundle install). Demonstrates building a 3D category chart in ~10 lines of Ruby with no C build tools.