With Jscript.NET more or less abandoned by Microsoft, there is an opening for a new JavaScript compatible language on the CLR. Fredrik Holmström is trying to fill the void with IronJS. Like the other Iron languages by Microsoft and independent developers, it is based on the Dynamic Language Runtime. This includes the DLR’s hosting framework and unified object model.
While still in the early stages, IronJS currently runs CLR 2 and Mono 2.6 and can compile jQuery 1.4. IronJS is being offered on github under the Microsoft Public License.