In a comment to an older, Javascript-related post of mine, Chris Zumbrunn has drawn attention to Helma, a Javascript Web Application Framework:

Helma is an open source web application framework for fast and efficient scripting and serving of your websites and Internet applications. Our goal is exactly what Mark described, taking that second pass at Javascript on the server-side by beginning to bridge the server- and client-side like you wouldn’t be able to do it when not using the same language “on both sides of the environment”.

I haven’t yet found the time to check it out, but it sure sounds intriguing.