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.NET implementations

Some common .NET implementations are

.NET Framework	The original .NET implementation whose first release was 2002. Runs on Windows only and is optimized for developing Windows desktop applications.
.NET Core	A cross platform implementation (Windows, Linux, macOS)
Mono	The runtime that powers Xamarin applications (Android, Mac, iOS, tvOS, watch OS) and Unity engine (games).
UWP	Targets touch-enabled Windows applications (on PCs, tablets, phablets, phones, XBox) and software for the Internet of Thigs (IoT).

.NET Core is distributed as a set of NuGet packages to individual applications.

The .NET Framework is installed in a system-wide location.

.NET Core is layered.

.NET Core does not have problematic technologies anymore, such as AppDomain or sandboxing.

In .NET Framework applications C# finalizers are called when the program exits - but not in .NET Core applications.

Components

An implementation includes the following mandatory or optional components

.NET Framwork has the CLR

.NET Core has CoreCLR and CoreRT

Some application frameworks are

.NET Standard .NET Standard is a list of APIs that must be present in a .NET implementation to claim compliance to a given .NET Standard version.

These APIs are implemented in the Base Class Library of a .NET implementation.

.NET Framwork implements the .NET Standard in version 4.5 and later.

This interactive chart allows to choose a .NET Standard version and then displays which .NET implementation supports the chosen version.