Not too sure what you mean by demonstrate responsive design?
If you’re trying to preview the sites on tablet/mobile, you can use the developer tools option in your browser. It should have a device preview option which should help quite a bit.
There are several sites like this one, but I see different results from site to site. Are there some that are more accurate than others for demonstrating responsive design?
Thanks
Personally i find the repsonsive views in the browser developer tools to be pretty darn accurate.
And if you’re using a Mac you can fire up Simulator which is part of their XCode plugin and run real world sims of iPads and iPhones – and that is 100% accurate.