Are there any .NET CLR/DLR implementations of ECMAScript?

Does anyone know of real (i.. no vaporware) implementations of ECMAScript targeting the .NET CLR/DLR ? Ideally something like what Rhino is for Java . A solid port of Rhino running on .NET Framework / Mono Framework would be perfect.

JSON left out Infinity and NaN; JSON status in ECMAScript?

Any idea why JSON left out NaN and +/- Infinity? It puts Javascript in the strange situation where objects that would otherwise be serializable, are not, if they contain NaN or +/- infinity values.