This is a library not a framework. It gives you full controll of building your app without making assumptions or templates of what you are building. Unlike Express, React or Rails, it does not provide router or controllers. It is a direct model to view connection.
Backbone provides a MV or Model View structure that allows data, that can be easily updated, on the client side server. It syncs to the database while the views are being rendered, allowing for a faster and more responsive user experience.
The biggest benefit of Backbone.js is the seperation of concern between the model and the view. Models manage internal data attributes and trigger "change" events. The view listens to the model react and re-render accordingly.
Backbone.js is one of the oldest MV libraries and is widely used amongst larger networks and corporations.
Download these dependencies
For older Internet Explorer support
http://backbonejs.org/#Getting-started
https://github.com/jashkenas/backbone/wiki/Tutorials%2C-blog-posts-and-example-sites