I've dug through their minified files and from what I can tell other than dependencies they use i.e. Backbone, underscore, jQuery, bootstrap, D3, etc I believe a lot of it is custom coded. It's truly incredible.
- React for DOM rendering
- D3 for visualization geometry
- RxJS for handling state (i.e. turning scroll position into animated properties)
- PIXI for WebGL bits (i.e. all the little circles moving around)