Microsoft's JScript is in a poor shape and is being deprecated. They'll probably build another interpreter on top of the DLR.<p>I don't know how good or complete the alternatives are though (probably not as mature as Rhino) ... <a href="http://github.com/fholm/IronJS" rel="nofollow">http://github.com/fholm/IronJS</a> ; <a href="http://jint.codeplex.com/" rel="nofollow">http://jint.codeplex.com/</a>