NOTE: This Backbone.js DocSet is now part of Dash!
A Backbone.js DocSet for use with Dash
Open Dash > Preferences > Docsets > Download Docsets; Click + and paste the following url:
Then click download next to the new item at the bottom of the list.
Clone the repository or download and extract the tarball from the downloads page. You should then be able to doubleclick the .docset package. You may want to move it into ~/Library/Application Support/Dash/DocSets/ or some other permanent location as it won't do this for you.