Ionic is an HTML5 mobile application development framework that comes with very native-styled mobile UI elements. Although Ionic is a young framework with its first alpha being released in late November 2013, its becoming a very popular framework with a fast-growing community of developers. 
Ionic’s goal is to close the gap between what native SDK on iOS or Android provides and is not available on the web. It offers a set of beautifully designed UI elements, layouts, and animations that make the development of hybrid applications easy and fast. Besides this, Ionic is built on top of AngularJS, which allows for minimal DOM manipulations and hardware accelerated transitions, making Ionic applications fast. Ionic comes with Sass and Apache Cordova under the hood, allowing for easy UI customizations and integration with device native services. 
The whole motivation behind Ionic could be explained by one of the slides from Adam Bradley, co-creator of Ionic. Figure 1 displays the gap Ionic targets – the missing web SDK.
Figure 2 shows multilayer architecture of Ionic applications.
Besides all the great built-in features such as pull-to-refresh or infinite scroll, Ionic also offers a very powerful CLI (command-line interface) that takes development to a whole new level. It allows one to create, test, and deploy application onto any platform. One can use features such as Ionic Lab that allows building and testing iOS and Android versions side-by-side, or LiveReload that instantly updates application every time changes in the source code are made, even if the application is running on a mobile device. This means one do not need to rebuild the application for a particular platform every time there are some changes in the source code. 
Ionic also comes with a great documentation and an open source icon library featuring over 440 icons. Besides this, the Ionic team have built the Ionic View application that allows one to distribute the application to testers and developers without having to go through app stores. They have also created Ionic Creator, an application that lets developers to build their applications with simple drag-and-drop components. And that is still not all, the team has recently released the Ionic Push service, which gives Ionic applications the ability to send native push notifications to devices on any platform. 
And there are still more features, such as Ionic Analytics which provides valuable insights into your application, Ionic Deploy that allows one to update and test applications on the fly, Ionic Playground that provides playground without the need to set up your development environment, or Ionic Market, an marketplace for addons, themes, and plugins.
As Adam Bradley announced at ng-conf 2015 , Ionic is planning to support the new version of AngularJS – AngularJS 2.0. With this in mind, and the fact that the company recently raised $2.6M , I believe that Ionic have a bright future in the mobile development world.
Onsen UI is an Ionic competitor that is built on top of AngularJS. Like Ionic, it also provides a set of UI elements that allows one to focus on the business logic of the application instead of inventing the wheel oneself. However, there are some small differences when compared with Ionic. First, Onsen UI uses a responsive layout, allowing for classic web development. Ionic, on the other hand, is not intended to be used for classic web development. Second, Ionic is a much more serious framework as it comes with powerful CLI and other useful tools that make development and deployment very smooth and fast. Third, Onsen UI has a much smaller community. [54, 55]
I briefly described three popular UI hybrid frameworks. I have to say that Ionic framework offers the most to developers and at the time of writing this article, it’s definitely the best framework when it comes to development of hybrid mobile applications. I value its powerful CLI and the use of Sass as a CSS preprocessor, Apache Cordova as a WebView framework, and the LiveReload feature that allows for rapid development.
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 Ionic: Advanced HTML5 Hybrid Mobile App Framework. URL: http://ionicframework.com/ (visited on 03/30/2015).
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 S. Perez. Drifty Grabs $2.6 Million To Turn Web Developers Into Mobile App Makers. 2015. URL: http://techcrunch.com/2015/03/30/drifty-grabs-2-6-million-to-turn-web-developers-into-mobile-app-makers/ (visited on 03/30/2015).
 famo.us. URL: http://famo.us/ (visited on 03/30/2015).
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 Onsen UI – A Custom Elements-Based HTML5 UI Framework. URL: http://onsen.io/ (visited on 03/30/2015).