enchant.js - A simple JavaScript framework for creating games and apps

enchant.js: 

• is a framework for developing simple games and applications in HTML5 + JavaScript
• was released in 2011, but has already had over 1,000 games and applications published
• is open source (MIT license), and therefore free to use
• has extensive supporting documents: API Documentation・Publications・Tutorial Site
• can be augmented with various plugins to increase functionality
• is continually developed and maintained by members of the Akihabara Research Center at UEI
• is now on reddit!

enchant.js - Features: 

• Objected Oriented: all items displayed are objects
• Multiplatform: runs in iOS, Android, Mac, Windows browsers
• Windows 8: supports development for Windows 8 interactive HTML5
• Event-driven: based on asynchronous processing via event listeners
• Animation Engine: allows the use of standard animation such as tweens
• Hybrid Drawing: supports drawing with both the Canvas API and the DOM
• WebGL Support: supports 3D games using WebGL with a plugin
• Content Library: includes a royalty-free image library for use in your games