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Updated
An engine specialized in 2D graphics, but designed more for people who know what they're doing. While it includes the ability to start developing a game immediately from a downloadable binary, it only supports using the FreeGLUT library on the desktop. It is designed in such a way that it expects the developer to be able to create the windowing system themselves. (or with a free library such as GLFW or SDL)
The main language used with Moai is Lua. Most of the time you shouldn't need to use C++ to extend the base engine, but the capability to do so is there. The documentation for the Lua codebase is kind of weak however, so you should be ready to do some searching to find out how to use various capabilities.
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Pros
Pro Is used by many pro developers
Moai SDK is used by popular developers including Double Fine for their mobile game, Middle Manager of Justice, and for their Kickstarter hit, Broken Age(formerly, Double Fine Adventure.) It was also used to create the popular mobile game Bubble Ball 2.
This proves that this engine can be used to make fully-featured and fun games.
Pro Helpful and detailed documentation
Although the Moai SDK is very advanced and uses complicated features, the documentation wiki thoroughly and clearly explains how to use these features, such as the Moai Cloud(a service that provides web services for your game), and multiple ways to build from source.