On: D3.compose – compose reusable charts and components with D3.js

The Atlantic's Quartz website has open-sourced a simple D3-based charting program called Chartbuilder. It's not as full-featured as Highcharts, but it's free at any usage level and customizable.

Code: https://github.com/Quartz/Chartbuilder

Try it: https://quartz.github.io/Chartbuilder/