Review is an awesome node.js package that uses PhantomJS to grab screenshots of all your websites in different screen resolutions.
It’s best said on the review Github page:
Updating large and possibly responsively designed sites can be a hassle. You never know whether your change breakes anything on the other end of your sitemap, or in a certain resolution, except if have a look at every individual page…in every resolution you care about.
Simply install review from the node.js package manager and feed it a JSON string of different websites and screen resolutions that you’d like to see them in. Highly recommended for anyone who needs to keep tabs on a responsive design, etc.
Install with the node package manager:
$ npm install -g review
Lots of detailed usage examples here.