PixiJS!

p5.js a JS client-side library for creating graphic and interactive experiences, based on the core principles of Processing.

Phaser is a fun, free and fast 2D game framework for making HTML5 games for desktop and mobile web browsers, supporting Canvas and WebGL rendering.

melonJS is an open source HTML5 game engine that empowers developers and designers to focus on content.

Part of the CreateJS group of libraries, EaselJS provides straight forward solutions for working with rich graphics and interactivity with HTML5 Canvas. It exposes an API that is familiar to Adobe Animate developers, but embraces JavaScript sensibilities. It consists of a full, hierarchical display list, a core interaction model, and helper classes to make working with Canvas much easier.

StageXL is an API for HTML5 game and application development that closely models and is nearly identical to the Adobe Flash API. It's built on the Dart programming language and offers an intuitive and complete library for impressive 2D content.