[MichaelGG]

Microsoft had a similar project called Volta: http://en.wikipedia.org/wiki/Microsoft_Live_Labs_Volta

It worked at the bytecode level - it wasn't just compiling C# into JS or something like that. I seem to remember that it had a full runtime in Javascript. It was terribly slow.

But, this kind of approach might not be so bad going forward, now that JS engines are faster. If the browser doesn't have a .NET runtime built-in, fallback to JS emulation.