Cocos2d-X is a game engine framework based on Cocos2d-iPhone, which consists of expanding supported platforms, with multiple choice of programming languages thats shares the same API structure. Programmers can choose to use their preferred language to achieve their targeted platform Native branch written in C++, with a little Java and Objective-C. Lua and javascript are binded as scripting language. HTML5 branch, also known as cocos2d-html5, is written in Javascript, that focuses on desktop browsers XNA port, is written in C#, focus on Windows Phone 7 and XNA. All the branches above are released under MIT License. With cocos2d-x framework, developers can easily create or port their games onto iOS, Android, Bada, BlackBerry Qnx, Marmalade, WindowsXP/Windows7, Linux and Windows8 Metro.
I have been developing games with cocos2d-x since it was in version 2.1.5 and have already published 2 games. The engine is great and is growing very fast!. Now the engine also allows 3D sprites and an IDE for lua and javascript, although I wish an IDE was built for c++. The community is also excellent.
The only downside I have faced is the lack of documentation, although right now the developers are putting up a great wiki. I myself struggled a lot during the learning phase.