Nodejs / rails / backbone architecture

I have an application that I create that works very much like Craigslist, but with disabilities. I usually used Rails for such an application, but I am interested in exploring the structure of nodejs / backbonejs, and it seems like a good opportunity to raise it.

I'm not sure how nodejs and / or backbonejs fit into this solution? I don't have to use rails, I'm fine using nodejs and backbonejs if that makes sense.

thank