The sound is using tone.js [0] (with a slight modification to make the tuning work).

The rest is built with - idyll (for the overall structure of the post) [1] - d3 with svg and canvas (for the tuner and visualizations) [2] - sketchapp and a plugin [3] to design the guitar

[0] https://tonejs.github.io/ [1] https://idyll-lang.org/ [2] https://d3js.org/ [3] https://github.com/mathisonian/sketch-interactive-export