A tool to help with responsive design
SlideRule helps with responsive development by showing five different page widths at the same time. This app gives you a handy little green icon in the corner of the omnibox. When clicked it will open up a new tab showing the site at different widths.*
The kicker is you can dynamically zoom between the pages with the arrow keys and spacebar. Also you can use chrome dev tools as usual(Just 5xDOM to sort through).
It works great with LiveReload if your using it in the actual page. The browser plugin will just reload the entire app.
*Pages that have X-Frame-Options set to 'deny' will not load. This includes Google's homepage.