GameJs is described as 'thin library on top of the HTML canvas element. In addition to the drawing functions it has a growing assortment of modules useful for game development' and is an app in the Development category. There are three alternatives to GameJs for Self-Hosted solutions and Online / Web-based. The best alternative is RingoJS, which is both free and Open Source. Other great apps like GameJs are Ajax Push Engine (Free, Open Source) and Webtendo (Free, Open Source).