What is Blazor? It’s a framework for browser-based (client-side) applications written in .NET, running under WebAssembly. It gives you all the benefits of a rich, modern single-page application (SPA) platform while letting you use .NET end-to-end, including sharing code across server and client.
Blazor is an experimental .NET web framework using C#/Razor and HTML that runs in the browser with WebAssembly. This is still in a very early stage of development, and if it the ASP.NET Core betas are anything to go by, we are in for a bumpy ride.