Whomever called JavaScript the assembly language of the web was a true prophet.

Compiling .Net code to JavaScript is not new. I have heard that Microsoft’s Office Web Apps, browser-hosted editing of Office documents, are built with Script#.

The difference with JSIL is that it compiles .NET Intermediate Language (IL), and therefore works with any .NET language – though note that:

JSIL is still in development. You will hit bugs

The screenshot says it all