We introduced .NET Core 1.0 on November 2014. The goal with .NET Core was to take the learning from our experience building, shipping and servicing .NET Framework over the previous 12 years and build a better product. Some examples of these improvements are side-by-side installations (you can install a new version and not worry about breaking existing apps), self-contained applications (applications can embed .NET, so .NET does not need to be on the computer), not being a component of the Windows operating system (.NET ships new releases independent of the OS schedule) and many more. On top of this, we made .NET Core open source and cross platform.
.NET Core 1.0 was primarily focused on high performance web and microservices. .NET Core 2.0 added 20K more APIs and components like Razor Pages and SignalR, making it easier to port web applications to .NET Core. And now .NET Core 3.0 embraces the desktop by adding WinForms, WPF and Entity Framework 6 making it possible to port desktop applications to .NET Core.
After .NET Core 3.0 we will not port any more features from .NET Framework. If you are a Web Forms developer and want to build a new application on .NET Core, we would recommend Blazor which provides the closest programming model. If you are a remoting or WCF Server developer and want to build a new application on .NET Core, we would recommend either ASP.NET Core Web APIs or gRPC, which provides cross platform and cross programming language contract based RPCs). If you are a Windows Workflow developer there is an open source port of Workflow to .NET Core.
With the .NET Core 3.0 release in September 2019 we think that all *new* .NET applications should be based on .NET Core. The primary application types from .NET Framework are supported, and where we did not port something over there is a recommended modern replacement. All future investment in .NET will be in .NET Core. This includes: Runtime, JIT, AOT, GC, BCL (Base Class Library), C#, VB.NET, F#, ASP.NET, Entity Framework, ML.NET, WinForms, WPF and Xamarin.
.NET Framework 4.8 will be the last major version of .NET Framework. If you have existing .NET Framework applications that you are maintaining, there is no need to move these applications to .NET Core. We will continue to both service and support .NET Framework, which includes bug–, reliability– and security fixes. It will continue to ship with Windows (much of Windows depends on .NET Framework) and we will continue to improve the tooling support for .NET in Visual Studio (Visual Studio is written on .NET Framework).
New applications should be built on .NET Core. .NET Core is where future investments in .NET will happen. Existing applications are safe to remain on .NET Framework which will be supported. Existing applications that want to take advantage of the new features in .NET should consider moving to .NET Core. As we plan into the future, we will be bringing in even more capabilities to the platform. You can read about our plans here.