I’ve recently started a project to provide an enhanced, extensible, embeddable interactive interpreter for multiple languages running on Node (including built-in support for CoffeeScript) here:
http://danielgtaylor.github.com/nesh/
It’s pretty basic at the moment but it already provides a nice base with multi-language support and an asynchronous plugin architecture, a small set of built-in utility functions, etc. Let me know if there are any specific features you are looking for 🙂