When comparing Crafty.js vs Rainbow, the Slant community recommends Crafty.js for most people. In the question“What are the best 2D game engines?” Crafty.js is ranked 30th while Rainbow is ranked 78th.
Ranked in these QuestionsQuestion Ranking
Easy to learn, based on Entities and Components, the later being class-like objects that entities inherit.
Has open function binding systems, allowing easy creation of custom components.
Pro Open source
Distributed under the MIT License.
Pro Written in modern C++, is scriptable in Lua
With support for Android, iOS, Linux, Mac OS X and Windows.
Pro Optional FMOD audio engine
Pro Supports Spine
Box2D integrated with Lua bindings.
Con No IDE
If you like having some huge GUI akin to Gamemaker, Unreal, Unity, etc, Crafty is not for you.
Con Not as feature-rich as other engines
Con Small community
Being fairly new on the scene, there aren't much of a community to speak of.