EaselJS

Advanced Flash-like library for HTML5 game and app development.

AGKSharp

AGKSharp is a free implementation of AppGameKit to be used with C# and .NET

Open-source JavaScript framework to create cross-platform and hybrid game engines, games, emulators, multimedia libraries and apps

Fabric.js is a powerful and simple Javascript HTML5 canvas library,

Free open-source JavaScript library for easily drawing HTML5 graphics and animation.

Desktop and Mobile HTML5 game framework. A fast, free and fun open source framework for Canvas and WebGL powered browser games.

Fast and flexible WebGL-based HTML5 game and app development library.

C++ and Java programming at the speed of thought.

Raphael.js is an Object Oriented drawing library. It is good at making in-depth diagrams with complex interactions.

Create 2D games and apps with the Flash-like API for the Dart programming language.

Practical framework for creating 3D Web applications

3D javascript engine for canvas and SVG

oCanvas is a JavaScript library intended to make development with HTML5 Canvas easier.