When ASP.NET first shipped as part of the.NET Framework in 2002, it was designed to make it easy for developers used to writing desktop applications to build Web applications with ASP.NET Web Forms. As the Web evolved, new frameworks were added to ASP.NET, including MVC in 2008, Web Pages in 2010, and Web API and SignalR in 2012.
This version of ASP.NET is a huge departure from its predecessors. Microsoft has rewritten ASP.NET from the ground up with modern framework techniques. The goal of this dramatic change is to improve the foundation of ASP.NET and make it cross-platform capable. The new stack is significantly smaller, lightning quick and open source for the world to review and contribute to.
ASP.NET 5 is a landmark release in many ways. It's full open source from the start, cross-platform and supported on Windows, Mac, and Linux. It includes contributions from the community and is being developed in the open on GitHub. ASP.NET 5 includes lots of great updates as well like TagHelpers, the unification of MVC and Web API, the componentization of the .NET Framework, dependency injection built in, an all-new project system, and deep client-side tooling for things like Bower, Gulp, and Grunt. This is an exciting time for the Microsoft web platform!