Dotnet core is a free, open-source, cross-platform, and general-purpose development platform for building various types of applications using .NET languages such as C#, F#, and VB.NET. It is a modular and lightweight framework that supports multiple operating systems, such as Windows, macOS, and Linux. It provides features such as high performance, security, interoperability, cloud integration, and more. It is developed and maintained by Microsoft and the .NET community.