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There is too much tool that can easily make games and mobile apps. Please refer to when you are wondering to develop on any platform.
I am writing about the proper use by purpose, and features of each tools(Monaca/Titanium Mobile/Unity).
Basically, to make the appearance in the HTML/CSS,and to implement the UI (such as buttons) by jQuary Mobile.
And we develop the app by write a javascirpt code.
Monaca is a convenient development environment because it furnished in the cloud base.
The disadvantage of Monaca, the operation of the application is slightly slow.Because it is based on HTML/CSS.
It is not suitable for application that require fast action.
When to use Monaca?
It uses when creating an app that will not change the remarkable future. In particular, it is best when you want to give top priority to development speed in the base with HTML.
Reference site about Monaca
I think the official documentation site is easy to understand most.
Platforms such as cloud linkage features are substantial, it is possible to develop a professional application with relative ease.
Image processing system is apparently not good, but it can be solved by writing code in Java/Objective-C as an external module.
When to use Titanium Mobile
Because the almighty, I am developing in Titanium Mobile basically. It is used for different scalability and maintenance of after, the Monaca and Titanium Mobile.
Reference site about Titanium Mobile
Unity is a 3D game engine.
I tried do make a 2D game and business tool app on Unity, but it is more good to use the Monaca and Titanium Mobile.
However, if you develop a 3D game, I recommend Unity. It has become a tool that specializes in 3D game development.
However, elements gambling basis is large market of mobile games. So, to think well before you enter.
I think Unity can be also applied to digital signage, and to watch trends.
When to use Unity
Unity is a 3D game engine in earnest. And it is difficult to develop 2D games and business tools in Unity.
However, there is an advantage of being able to unify the user interface, regardless of the platform differences.
Reference site about Unity