The MEAN stack is a popular technology stack used in web development, particularly for building dynamic and modern web applications. MEAN is an acronym that stands for:

MongoDB: A NoSQL database that uses a document-oriented data model. MongoDB stores data in flexible, JSON-like documents, making it suitable for handling diverse data types and schemas.

Express.js: A minimalist and flexible web application framework for Node.js. Express.js simplifies the process of building web servers and handling HTTP requests and responses.

Angular (or AngularJS): A front-end JavaScript framework maintained by Google. Angular is used for building dynamic and interactive user interfaces. It provides a comprehensive set of tools and features for building single-page applications (SPAs), including data binding, dependency injection, routing, and component-based architecture.

Node.js: A server-side JavaScript runtime environment built on the V8 JavaScript engine. Node.js enables developers to run JavaScript code outside of a web browser, making it possible to build server-side applications using JavaScript. It offers event-driven, non-blocking I/O model, which is well-suited for building scalable and real-time web applications.

The MEAN stack is useful in web development for several reasons:

Full JavaScript Stack: The Mean Stack Development allows developers to use JavaScript for both client-side and server-side development. This reduces context switching and streamlines the development process, as developers can work with a consistent language and ecosystem across the entire stack.

Real-Time Capabilities: Node.js, with its event-driven architecture, enables real-time communication between the client and server, making it ideal for applications requiring instant updates or live data streaming.

Scalability and Performance: MongoDB and Node.js are designed for scalability and high performance, making them suitable for building applications that need to handle large volumes of data and concurrent requests efficiently.

Rapid Prototyping and Development: The MEAN stack's modular architecture and extensive set of tools and libraries allow for rapid prototyping and development of web applications. Developers can leverage pre-built components and modules to accelerate development and focus on building application logic.

Community Support and Ecosystem: Each component of the MEAN stack has a large and active community of developers, contributors, and resources. This provides access to a wealth of documentation, tutorials, libraries, and frameworks, making it easier for developers to troubleshoot issues, learn new concepts, and stay updated with best practices in web development.

While the exact internal workings of major companies are often not publicly known, the MEAN stack's popularity makes it a strong possibility for several web applications you might use every day. Here are some examples of applications that could be built with MEAN:

• Single-Page Applications (SPAs): Many modern web applications are SPAs, meaning they load a single HTML page and update content dynamically without full page reloads. The MEAN stack's JavaScript-heavy architecture makes it a good fit for these types of applications.
• Social Media Platforms: Social media applications heavily rely on real-time updates and user interactions. The MEAN stack's ability to handle dynamic data and user interactions efficiently makes it a potential choice for such platforms.
• E-commerce Stores: While some large e-commerce platforms might have custom backends, the MEAN stack offers a strong solution for smaller to mid-sized online stores. It can manage product data, user accounts, and shopping carts effectively.
• Real-time Collaboration Tools: Tools like Google Docs or Trello that allow multiple users to work on documents or projects simultaneously could potentially be built with the MEAN stack. The framework's ability to handle real-time communication between users makes it a suitable candidate.

It's important to remember that these are just examples, and the specific technologies used by major web applications are not always publicly available information. But the strengths of the MEAN stack – its JavaScript-based architecture, efficiency with dynamic data, and potential for real-time features – make it a compelling choice for many web applications you encounter online.