• .NET Core is the future of .NET: If you’ve already started working with .NET Core, that’s great! If you’re starting a new project, you should consider .NET Core.
• .NET Framework will continue to be supported: If you have any existing applications on .NET Framework (Windows-only), you can keep those on .NET Framework.
• .NET Releases will become more predictable: Starting with .NET 5.0, there will be 1 major release every year,  after which each even-numbered release (6.0, 8.0, etc) will come with LTS (Long-Term Support). 

.NET Developer Updates from Build 2019 

What Does .NET 5 Mean To You 

.NET 4.8 is the end of the road for .NET Framework.
.NET 5 = .NET Core vNext

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.  

  There are several issues with consuming .NET Standard libraries that were built for those versions from .NET Framework 4.6.1 projects. For .NET Framework projects that need to use such libraries, we recommend that you upgrade the project to target .NET Framework 4.7.2 or higher. 

Updates to .NET Framework 4.8 on Windows 8.1, Server 2012 R2, Server 2012, Windows 7 SP1, and Server 2008 R2 SP1 will continue to be delivered outside of the Windows cumulative update through the existing .NET Framework updates. 

The .NET Framework 4.8 includes an updated toolset as well as improvements in several areas:

• [Runtime] JIT and NGEN Improvements
• [BCL] Updated ZLib
• [BCL] Reducing FIPS Impact on Cryptography
• [WinForms] Accessibility Enhancements
• [WCF] Service Behavior Enhancements
• [WPF] High DPI Enhancements, UIAutomation Improvements 

First it is important to recognize that the .NET Framework is not the same as .NET Core. The .NET Framework is effectively now in maintenance mode , and all innovation is occurring in the open source .NET Core now and into the future. So step one to remaining relevant is to understand .NET Core (and the closely related .NET Standard).