Chart.js

Pass it data and options, get a canvas-rendered chart. Done.

This is the most popular charting library on the web for a reason: it works, it's simple, and it looks good out of the box. Animation, tooltips, legends, responsive sizing, all built in. Eight chart types cover 90% of dashboard needs.

MIT, fully free. No paid tier. Has been around since 2013 and isn't going anywhere.

The catch: Chart.js renders to canvas, not SVG. That means you can't style individual elements with CSS, can't easily make charts accessible to screen readers, and complex interactions (clicking on specific data points, custom hover behaviors) require more work than SVG-based libraries. If you need highly customized, interactive data visualizations, D3.js gives you full control. If you need standard charts that look good fast, Chart.js is the answer.