[meekins]

Windows actually has a Javascript (well, the JScript dialect of ECMAScript) interpreter out of the box in the form of Windows Script Host. It also supports VBScript. You can play with it on the command line using the cscript command.

[PeCaN]

The most interesting part is that you can script applications with it. I recall writing a script that played Google's running game during the Olympics a while back when I was learning to program.