You can then use its scaffold generator to create a full-featured CoffeeScript implementation based on your model. Its form generation matches all model attributes to text inputs, unlike Rails' own scaffolding, which uses more appropriate input types when possible. But it does accept attributes, which is convenient.
Confusingly, the gem for codebrew/backbone-rails is named rails-backbone. This is not a typo in the Readme.
aflatter/backbone-rails also appeared in May 2011, apparently just after codebrew's project. It is minimalist, consisting of a simple installer that copies backbone.js and dependencies into your project, along with a little Sprockets manifest for the asset pipeline. At the time of this writing it still uses the latest release of Backbone. Don't discount it, because it may be exactly all that you need.
meleyal/backbone-on-rails arrived today, and already has over 100 GitHub watchers, as well as a mention on Hacker News. It distinguishes itself from its predecessors by following the directory and code organization conventions laid out in thoughtbot's Backbone.js on Rails ebook. (The book costs $49 for a single reader, but you can view the conventions in the sample chapter).
Here's what the install output looks like:
And this is what the scaffold output looks like:
The scaffolded files are empty apart from their class declarations, but I imagine that will change in later releases. You may consider the blank state a good thing. Regarding directory structure, I think the important difference from codebrew/backbone-rails is that meleyal/backbone-on-rails makes the assumption that you will only be using one client-side MVC framework. A good assumption that leads to a simpler directory structure.