Fitgrd is a responsive and lightweight css grid system, especially made for rapid prototyping. Love how the site pretty much demonstrates the product.
This website has unfortunately been redesigned or gone offline, so I have removed the direct link to it. The screenshot below hopefully preserved enough of the design but if you are really keen to inspect further, try this Archive.org link. FYI: the site was first featured on 13 May 2013.
Published 13 May 2013