The Responsinator helps website makers quickly get an indication of how their responsive site will look on the most popular devices. It does not precisely replicate how it will look, for accurate testing always test on the real devices.
We recommend using Chrome on OSX 10.7+ with scroll bars set to "when scrolling" (System Preferences › General › Show scroll bars › "when scrolling"). This means the device widths aren’t affected by scroll bars.
Pro tip: append &scroll=ext to move the scroll bars outside of the device frame.
We're currently building this feature. Having your own Responsinator will cost $6USD per month, or $50USD per year.
Email email@example.com for more details.
It means designing your website to adapt to the user's viewing environment (mobile, tablet, laptop etc.). It does this through the use of media queries, and other clever technology. Ethan Marcotte wrote the original article about it, and a pretty handy book.
If you have a non-responsive, fixed width site and you'd like to get an idea of what it looks like on these
devices add &fixed_width=x to the end of the URL where x is the width of your site.