sigma.js
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sigma.js is a javascript library for drawing graphs, the dots-and-lines kind, not charts. it draws with WebGL, so it can handle thousands of nodes and edges without the page choking.
sigma doesn't store the graph itself. it renders a graphology graph, which keeps the data and the drawing separate. you build the graph in graphology, hand it to sigma, and sigma takes care of the canvas, labels, zooming, panning and mouse events.
it's open source (github), made by Alexis Jacomy and Benoît Simard at OuestWare, with Guillaume Plique from the Sciences Po médialab, who also maintains graphology.
v4 came out in october 2026 and changed a lot. styling moved to style rules and node states instead of "reducer" functions, and the camera api got renamed bits. most examples online are still v3, so read the migration guide first.
it's what draws the graph on this site, see How I Built the Graph.