.NET is a free, cross-platform, open source developer platform for building many different types of applications. With .NET, you can use multiple languages, editors, and libraries to build for web, mobile, desktop, gaming, and IoT. Whether you’re working in C#, F#, or Visual Basic, your code will run natively on any compatible OS. .NET implementations include:
.NET Core is a cross-platform .NET implementation for websites, servers, and console apps on Windows, Linux, and macOS.
.NET Framework supports websites, services, desktop apps, and more on Windows.
Xamarin/Mono is a .NET implementation for running apps on all the major mobile operating systems.