Impact is an HTML5 Game Engine. More info & documentation: http://impactjs.com/
Various example games to get you started are available on http://impactjs.com/download
Impact is published under the MIT Open Source License. Note that Weltmeister (Impact's level editor) uses jQuery which comes with its own license.