ASP.NET Core is an open source web framework for building modern web applications that can be developed and run on Windows, Linux and the Mac. It includes the MVC framework, which now combines the features of MVC and Web API into a single web programming framework. ASP.NET Core is built on the .NET Core runtime, but it can also be run on the full .NET Framework for maximum compatibility.
ASP.NET Core is a reinvention of the ASP.NET web frameworks. From the beginning of ASP.NET in 2002 the .NET server-side frameworks have been built around the concepts of modules, handlers, and integration with Internet Information Server (IIS) on Windows. With ASP.NET Core, we have rewritten the web framework and .NET framework to better enable a modern web development experience and provide a baseline to build the next 15 years of server development. By removing modules and handlers, which are IIS concepts, we can make ASP.NET Core run great on other web servers like Nginx and even in your own hosted application. All application development for ASP.NET Core is built around a new middleware definition and a Controller-centric approach.