What is ASP.NET 5?
ASP.NET 5 is entirely new open source web application stack for .NET from Microsoft. It designed to meet the need for modern server web applications and it is optimized for modern development workflow. ASP.NET 5 continuous to run on .NET Framework but also run on new framework called .NET Core.
ASP.NET 5 on .NET Framework
You can continue to run all your applications on .NET Framework using APIs and existing packages. .NET Framework is installed machine wide and it is part of with the updated operating system. You can run your ASP.NET 5 applications on cross-platforms like mac and Linux via mono.
ASP.NET 5 on new .NET Core Framework
.NET Core CLR runtime is a new framework which is specially optimized for server workloads which occupies much smaller footprint both on disk and memory. The Framework APIs that you are used in your applications all come in as NuGet packages.
.NET core itself including the runtime and those packages can be installed bot side-by-side with different versions of themselves. Application, runtime and framework deploys as a whole can be deployed as single portable unit.
*It is cross-platform that can run on windows, mac and Linux for both development and production.
Running ASP.NET 5 application on .NET Core
The project.json file looks as in the following screenshot
In Startup.cs file you need to change the code to run under .NET core framework.
You can change the context of the C# file using the drop-down shown in the above picture. Depending on the targeting of the framework you will get intellisense and errors for the file. The following change in Startup.cs file allows you to run the application on both frameworks.
In the debug tab of your application, you can actually target the .NET core framework as shown in the following picture
For more information about ASP.NET 5 and .NET Core Framework you can visit the following link