Try ReoScript, an open-source JavaScript interpreter implemented in C#.
ReoScript makes your application can execute JavaScript. It has a wide variety of extension methons such as SetVariable, Function Extension, using CLR Type, .Net Event Binding and etc.
Hello World:
ScriptRunningMachine srm = new ScriptRunningMachine();
srm.Run(" alert('hello world!'); ");
And here is an example of script that creates a winform and show it.
import System.Windows.Forms.*; // import namespace
var f = new Form(); // create form
f.click = function() { f.close(); }; // close when user clicked on form
f.show(); // show