How is that light weight? let's see it has scripts for skeloton projects/models/etc, has it's own orm's, and even ships with its own package manager. that seems like a lot of stuff is you're looking to light weight.
Look at the description:
"Monorail.js will never force you to install anything not needed for your project. The goal is to use what you need."
Plus, it's definitely lighter than express.
I think if I were to use a node MVC framework built on express, I'd go with Matador: http://obvious.github.com/matador/