React.js is a JavaScript library used for building user interfaces, particularly for web applications. Developed by Facebook, it follows a component-based architecture, where UIs are composed of reusable and independent components. React utilizes a virtual DOM to efficiently update the actual DOM, resulting in improved performance.

One of its key features is the ability to create reusable UI components, making development more modular and maintainable. React employs a declarative programming style, allowing developers to describe the desired UI state, and React handles the updates automatically.

It embraces unidirectional data flow, promoting better predictability and easier debugging. React's ecosystem is vast, with tools like React Router for routing, Redux for state management, and React Native for building mobile applications.

Its popularity stems from its flexibility, performance, and extensive community support. So we will develop a real time application with react app using with API which developed with PHP and MySQL phpmyadmin