flixel is a free Actionscript (Flash) library that I distilled from a variety of Flash games that I've worked on over the last couple years, including Gravity Hook, Fathom and Canabalt. It's primary function is to provide some useful base classes that you can extend to make your own game objects.
Godot Engine – Multi-platform 2D and 3D game engine
JavaScript 3D Library.
The HTML5 Creation Engine: Create beautiful digital content with the fastest, most flexible 2D WebGL renderer.
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.
Open-Awesome is built by the community, for the community. Submit a project, suggest an awesome list, or help improve the catalog on GitHub.