Emmet Re:view is a Chrome extension which displays responsive websites in multiple views, side-by-side, enabling you to test how they work with different devices and resolutions.
Visit the test website, click Emmet Re:view, and a tab opens with resizable views for each CSS media query breakpoint of your page. (Keep in mind that if this isn't a responsive website and there are no breakpoints, they'll all look the same.)
Scroll through any of these viewports, move, hover and click the mouse, and Emmet Re:view keeps the other views synced.
You can additionally resize an individual viewport to see how the site behaves.
The extension also provides a Device Wall which displays multiple device-sized viewports for every <meta name="viewport"> tag of your page.
You're then able to select various devices presets - "Android phones", "Android tablets", "Apple phones", "Apple tablets", individual device types - and see how the site will look at that resolution.
A simple and lightweight way to test responsive websites at different resolutions.