What's Godot Game Engine
Godot is a fully featured, open source, MIT licensed, game engine. It focuses on having great tools, and a visual oriented workflow that can export to PC, Mobile and Web platforms with no hassle. The editor, language and APIs are feature rich, yet simple to learn, allowing you to become productive in a matter of hours.
URLs:https://github.com/okamstudio/godothttp://www.godotengine.org/wp/Why Godot + Live2D
Godot is great for inide game developers, it's free and powerful. As Godot will be reach stable 1.0 in june, it'll getting more attention as it deserved. Godot is highly extendable, Live2D would be greate candidate to be added as a Godot Module. More indie game developers start using Godot, more games got the chance to use amazing Live2D techology in their games!
I just take a glance at Cocos2d-x SDK, it seems a great starting point to make it more generic C++ SDK other than Cocos2d-x specific, and would also server as greate starting point to port to Godot ( or other plug-able Game Engine.