What is .NET?

.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, games, and IoT.

Languages
You can write .NET apps in C#, F#, or Visual Basic.

C# is a simple, modern, object-oriented, and type-safe programming language.
F# is a cross-platform, open-source, functional programming language for .NET. It also includes object-oriented and imperative programming.
Visual Basic is an approachable language with a simple syntax for building type-safe, object-oriented apps.

Cross Platform
Whether you're working in C#, F#, or Visual Basic, your code will run natively on any compatible OS. Different .NET implementations handle the heavy lifting for you:

.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.

One consistent API
.NET Standard is a base set of APIs that are common to all .NET implementations.
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Each implementation can also expose additional APIs that are specific to the operating systems it runs on. For example, .NET Framework is a Windows-only .NET implementation that includes APIs for accessing the Windows Registry.