FossFLOW is a powerful, open-source Progressive Web App (PWA) for creating beautiful isometric diagrams. Built with React and the Isoflow library, it runs entirely in your browser with offline support.
Vega-Altair is a declarative visualization library for Python. Its simple, friendly and consistent API, built on top of the powerful Vega-Lite grammar, empowers you to spend less time writing code and more time exploring your data.
In semi-related news, is pretty impressive.
A general purpose real-time charting library for building beautiful, smooth, and high performance visualizations.
Interactive Geometry, plotting, visualization
JSXGraph is a cross-browser library for interactive geometry, function plotting, charting, and data visualization in a web browser. It is implemented completely in JavaScript, does not rely on any other library, and uses SVG, VML, or canvas. JSXGraph is easy to embed and has a small footprint: less than 100 KByte if embedded in a web page. No plug-ins are required! Special care has been taken to optimize the performance.
Peity - Little charts for little projects...
Elycharts is a pure javascript charting library, easy to use and completely customizable.
Highcharts is a charting library written in pure JavaScript, offering an easy way of adding interactive charts to your web site or web application. Highcharts currently supports line, spline, area, areaspline, column, bar, pie and scatter chart types.