Why Use Aura?
Aura comes with a rich and extensible component set to kick start building apps. You don't have to spend your time optimizing your apps for different devices as the components take care of that for you.
The framework intelligently utilizes your server, browser, devices, and network so you can focus on the logic and interactions of your apps.
Developing with Aura
You can build your user interface at a granular level and easily integrate with popular toolkits and libraries, such as jQuery. Aura's lightweight and scalable architecture uses two key building blocks: components and events.
Components use markup that looks similar to HTML. You can also use HTML or any other code that can execute within an HTML page. Components are encapsulated and their internals stay private. You can extend existing components to customize their behavior.
The robust event model enables you to develop loosely coupled components. Once you define the events that interact with your components, your team can work on the components in parallel to quickly build a powerful app.
Aura also supports a powerful expression language, embedded testing, performance, and security features.
Aura On the Salesforce Platform
The Aura framework has been implemented on the Salesforce platform in a variety of ways. Initially this became the UI framework of choice for Salesforce R&D including features such as the Salesforce1 mobile app, Chatter Feed, the
analytics:reportChart Visualforce tag, and many more.
The implementation of Aura on the Force.com Platform has now become Lightning Components and Lightning App Builder, along with several related features. For questions related to these, please do not use the Aura tag. This should be reserved for the open source framework only.