The new ASP.NET 5 Runtime is described by Daniel Roth:
As you saw back in December, ASP.NET 5 is based on a flexible, cross-platform runtime host that can host one of several .NET CLRs. You can run ASP.NET 5 applications on the .NET Framework with its full API set for maximum compatibility. You can also run ASP.NET 5 on the new .NET Core, which enables true side-by-side deployments that you can copy into existing environments without having to change anything else on the machine. In the future, you’ll also be able to run ASP.NET 5 cross-platform on .NET Core, and there’s community support for running cross-platform on Mono today.
The runtime hosting infrastructure for ASP.NET 5 is currently called the K Runtime Environment (KRE), which is a generic placeholder name until we finalize the official name. The KRE provides an environment that has everything a .NET app needs to run: a host process, CLR hosting logic, managed entry point discovery and so forth. The KRE was built for running cross-platform .NET Web applications, but it can run other types of .NET applications, too, such as console apps. The KRE is based on the same .NET CLR and base class libraries .NET developers have come to know and love, while enabling cross-platform support for running .NET applications on Windows, OS X and Linux.
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