.NET Core is an open-source, cross-platform framework developed by Microsoft for building modern applications. It allows developers to create applications that can run on various operating systems, including Windows, macOS, and Linux. This flexibility makes it a popular choice for web, mobile, and cloud-based applications. One of the key features of .NET Core is its modular architecture, which enables developers to use only the necessary components for their projects. This results in smaller application sizes and improved performance. Additionally, .NET Core supports multiple programming languages, including C#, F#, and Visual Basic, making it accessible to a wide range of developers.