Responsivator, another useful open source online tool that helps people to render a website in different screen sizes, best for responsive website debug use.
You can set any screen size you want Responsivator to render for you, default views it have 480×320 for phone, 800×480 for small tablet, 1024×768 for big tablet and 1280×800 for desktop. Click the ‘customize’ button to add new resolutions.
Thanks John Polacek who made this and maintaining this great and handy online tool for free.
Source: Read more about Responsivator