Backbone happens to be a single script, and is monolithic in that sense ... but really, it's just a library that provides "specific functionality".
There are many sites that just use Backbone Models, or just Views, or just the Router, all in isolation. Some use the Models on the server-side ... some use the Views in conjunction with Handlebars.js, or jQuery.tmpl, or Eco, or what have you.
I encourage you to browse the list of example sites -- there's really a huge variety of uses you can observe: http://backbonejs.org/#examples
There are many sites that just use Backbone Models, or just Views, or just the Router, all in isolation. Some use the Models on the server-side ... some use the Views in conjunction with Handlebars.js, or jQuery.tmpl, or Eco, or what have you.
I encourage you to browse the list of example sites -- there's really a huge variety of uses you can observe: http://backbonejs.org/#examples