D3.js (D3 for Data-Driven Documents) is a JavaScript library for producing dynamic, interactive data visualizations in web browsers. Developed by Mike Bostock
License: Open Source
D3.js offers unparalleled customization and flexibility for complex data visualizations, making it ideal for developers who need fine-grained control. In contrast, Highcharts provides an easier-to-use API with a variety of pre-built chart types, making it better suited for quick implementations and businesses needing commercial support.