ASP.NET Core is an open-source and cross-platform web framework developed by Microsoft for building modern web applications. It is a complete rewrite of the original ASP.NET framework and has been designed to be lightweight, modular, and highly performant.

ASP.NET Core is built on top of the .NET Core runtime, which allows it to be run on Windows, macOS, and Linux. This cross-platform compatibility makes it a popular choice for developers who want to build web applications that can be deployed on different operating systems.

One of the key advantages of ASP.NET Core is its performance. It has been optimized for high throughput and low latency, making it ideal for building scalable and responsive web applications. It also supports asynchronous programming, which allows for efficient handling of multiple concurrent requests.

Another key feature of ASP.NET Core is its modularity. It follows a modular architecture, where functionality is organized into self-contained components called middleware. This modular approach makes it easy to add or remove functionality as needed, and also allows for better testability and maintainability of the codebase.

ASP.NET Core also includes a powerful and flexible dependency injection system, which makes it easy to manage and inject dependencies into your application. This promotes loose coupling and allows for better separation of concerns, making your code easier to test and maintain.

ASP.NET Core supports a wide range of development scenarios, including web applications, web APIs, and real-time applications using technologies like SignalR. It also provides a rich set of tools and libraries for building modern web applications, including built-in support for popular frontend frameworks like Angular and React.

Overall, ASP.NET Core is a powerful and versatile web framework that offers high performance, cross-platform compatibility, modularity, and a wide range of tools and libraries for building modern web applications. It is a popular choice for developers looking to build scalable and responsive web applications using the .NET platform.