The .NET Core Framework is a free, open-source, cross-platform framework for building modern applications. It was created by Microsoft and released in 2016 as a successor to the .NET Framework. The .NET Core Framework provides a set of tools and libraries that developers can use to build applications for Windows, macOS, and Linux operating systems.

Some of the key features of the .NET Core Framework include high performance, modularity, and scalability. It also includes support for popular programming languages like C#, Visual Basic, and F#.