Im getting into Backbone.js to structure the javascript code for my project and I love HAML for templating on the backend(rails), so Id like to use it for Backbone Views templat
Check out Middleman. It includes haml, sass, coffee, slim, etc. It uses gems like rails does and has a lot of other awesome functionality.
http://middlemanapp.com/
They even have a custom extension for backbone, https://github.com/middleman/middleman-backbone
It also allows you to build it into static html, css, and js for super fast loading.