Check out http://bower.io/ :

> Bower is a package manager for the web. It offers a generic, unopinionated solution to the problem of front-end package management, while exposing the package dependency model via an API that can be consumed by a more opinionated build stack.

rails-assets is an example of a higher-level, more opinionated stack that adds value on top of bower.

Among other things, Bower lacks the equivalent of Gemfile.lock or npm-shrinkwrap.json.

So you can't get reliably repeatable installs.

Rails Assets:

- creates manifest files for each component so you can just "require jquery" instead "require jquery/dist/jquery"

- splits assets in four categories: javascripts, stylesheets, images, fonts, so you can use sprockets helpers without a problem

- replaces relative urls in stylesheets with image-url font-url etc., so assets work out of the box

- converts .css files to .scss so you can get advantage of @import in SASS files

- you get assets locking with Gemfile.lock, so you can be sure each deploy will look the same. It's not possible yet with bower.

And few other sprockets integrations.

Unfortunately it's centralized solution but we're working on that.

I guess the idea would be that you could keep everything in your Gemfile. Personally, I'm fine with just using Bower for the front end pieces.