.NET
.NET is a free, cross-platform, open source developer platform
.NET implementation
- .NET 5 (and .NET Core) and later
- .NET Framework
- Mono
- UWP
.NET Framework
.Net Framework is the original .NET implementation that has been around since 2002. Versions 4.5 and later implement .NET Standard, so code targeting .NET Standard will run on these versions of the .NET Framework. It also includes some Windows-specific APIs, such as those for Windows desktop development through Windows Forms and WPF. The .NET Framework is well suited for building Windows desktop applications.
Mono
Mono is the .NET implementation used primarily when a small runtime is required. It's the runtime that drives Xamarin apps on Android, macOS, iOS, tvOS, and watchOS, and is primarily aimed at a small memory footprint. Mono also supports games generated using the Unity engine.
It supports all currently released versions of .NET Standard.
UWP
UWP is a .NET implementation for building modern touch Windows applications and software for the Internet of Things (IoT)
.NET Standard
.NET Standard is a set of formal .NET API specifications for multiple .NET implementations
The motivation behind .NET Standard is to improve consistency in the .NET ecosystem