Cocos2d is an open source software framework. It can be used to build games, apps and other cross platform GUI based interactive programs. Cocos2d contains many branches with the best known being Cocos2d-objc, Cocos2d-x, Cocos2d-html5 and Cocos2d-XNA.
Cocos2d-X is for developers who wish to make cross-platform games.
In particular, Cocos2dx is for developers who want to use an open-source game engine. There's a thriving community of Cocos2dx developers who are helping each other succeed through online forums and sites like Stack Overflow.
The high price tag and limiting nature of closed-source engines such as Unity and Corona are what cause many a developer to choose open-source.
Another key reason to use an open-source game engine is that you can modify anything if necessary.
MaterializeCSS is a modern responsive front-end framework based on Material Design. It simplifies life for developers and the users they serve.
It is Created and designed by Google, Material Design is a design language that combines the classic principles of successful design along with innovation and technology.
Standard CSS with minimal footprint.
Includes new versions of common user interface controls such as buttons, check boxes, and text fields which are adapted to follow Material Design concepts.
Includes enhanced and specialized features like cards, tabs, navigation bars, toasts, and so on.
Cross-browser, and can be used to create reusable web components.
PhoneGap is a free and open source framework that allows you to create mobile apps using standardized web APIs for the platforms you care about.
When packaged for deployment, the PhoneGap application is a binary distributable file that can be distributed by the “normal” application marketplaces (iTunes, Google App Market, Amazon Market, etc…).
PhoneGap can be used to build applications that target multiple platforms, including Apple iOS, Google Android, Windows Phone, BlackBerry, HP WebOS, Symbian, and Bada.
Since the UI rendering engine is the mobile device’s web browser, PhoneGap applications can literally look like anything.
You can use standard HTML & CSS to make it look like a normal web page, you can use a UI framework like jQuery UI, Kendo UI, Sencha, Twitter Bootstrap, or Skeleton (or any other HTML/CSS/JS user interface framework). You can also use CSS styles/themes to make your web content look like native apps, such as iUI to mimic iOS or Android, or bbUI to mimic BlackBerry.
It depends upon the specific application, user experience design, target audience, and use cases to dictate how a PhoneGap application will appear.