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 is primarily focused on data-driven documents and provides powerful tools for creating complex data visualizations, while Processing.js is designed for creative coding and artistic expression, making it more suitable for visual art and animations. D3.js has a steeper learning curve but offers more flexibility with data, whereas Processing.js is easier for beginners and emphasizes ease of use in creating visual content.