.NET Standard 2.0 is final

This /is/ geared heavily towards improving the .NET Core story. The purpose of this spec is to provide library authors with a set of APIs that they can expect will exist on .NET Standard 2.0-implementing runtimes (a list of which are supplied). This allows library authors to write code that works when deployed across multiple implementations and it allows application writers to trust that their dependencies will work on the platform of their choice.

Two major implementations of .NET Standard 2.0 are the traditional .NET Framework and .NET Core, so libraries targeting .NET Standard 2.0 can be used on both platforms without modification.

So just so I'm clear,

.NET ECMA Spec ⊆ .NET Standard ⊆ (.NET Core ∩ Mono ∩ Xamarin ∩ Unity) ⊆ .NET Core ⊆ .NET Framework

Correct?

Microsoft's Xamarin Forms 3.0 (stable release later this year) allows you to target Linux and Mac[1] and is very similar to UWP conceptually - UI written once, run anywhere. It's just that Xamarin's "anywhere" is much larger :)

Disclosure: I work on Xamarin team at Microsoft

[1]https://forums.xamarin.com/discussion/85747/xamarin-forms-fe...

For people confused about what .NET Standard is and how it relates to .NET Core:

Here's an FAQ: https://github.com/dotnet/standard/blob/master/docs/faq.md Here's a series of short videos from the product team explaining it: https://www.youtube.com/playlist?list=PLRAdsfhKI4OWx321A_pr-...

Short excerpt from the FAQ:

  .NET Standard is a specification that represents a set of APIs that all .NET platforms have to implement. This unifies the .NET platforms and prevents future fragmentation. Think of .NET Standard as POSIX for .NET.

  Having a standard solves the code sharing problem for .NET developers by bringing all the APIs that you expect and love across the environments that you need: desktop applications, mobile apps & games, and cloud services.

Conceptually, I think of it in terms of browsers and browser standards. The relationship between .NET Standard and the various .NET platforms (.NET Core, .NET Framework, Mono, Xamarin, UWP, etc.) is similar to HTML specifications (e.g. https://www.w3.org/TR/html5/) and individual browsers. Newer HTML features are available on newer browsers, and some browser feature implementation is contextualized (e.g. some web features don't make sense on a mobile phone browser). I know there are rabbit holes to #wellactually on that, so if it doesn't work for you don't worry about it, but as an analogy I've found it helpful.

Having a defined feature matrix makes it easier to see which APIs are available for a given platform and version.

(Microsoft employee, .NET team member, Nazgûl)

ECMA spec is for the CLI, essentially the specification for runtime like type system and GC and all the other things that make an environment work at all

Net Standard is a specification of APIs. So in order to be compliant to the standard you must have a class named X with parameters string Y, int Z.

"Net Framework" is the name for the Windows "full .net framework" -- this doesn't have a descriptive name since it was before all the rest, but basically its an SDK that is a superset of the Net Standard (and therefore is .Net Standard compliant / interoperable)

Mono is a open source implementation of "Net Framework" that runs on multiple platforms (linux, etc). It attempts to treat full .NET Framework's surface area as a spec but re-implement it cross platform. It is _also_ a open source CLI implementation. So in common speech "mono" like ".net" can refer to either the "basic sdk" _or_ the runtime environment.

Xamarin is forks of mono for iOS, Android and Mac platforms plus libraries that include full support for interacting with those platforms Native SDKs

Unity is a fork of Mono plus gaming tooling and runtime tools. Microsoft does not maintain this, it's a separate company.