PixiJS is a 2D Graphics Rendering framework for the web. It was created by Matt Groves to normalize the canvas and webgl APIs into a simple scene graph originally modeled loosely on the Flash API. Its primary focus has always been on performance so that it is really fast. Because of this it is primarily a webGL rendering surface with canvas 2d fallback.
To get PixiJS and read more about it you can visit its website pixijs.com. There they have download links examples and other resources for learning as well as a link to the github repository to keep up to date with its development.
Check out the Bunny Mark performance test to get an idea of how fast Pixi is.
You can find the code used for the video intro below.