Foundation: HTML/CSS boilerplate that responds to changing screen dimensions
foundation.zurb.com
foundation.zurb.com
But please, tell me why I should use this rather than Skeleton (http://getskeleton.com/) or Twitter's Bootstrap (http://twitter.github.com/bootstrap/)?
From a brief read Foundation explicitly supports nested grids, it's handling of centering columns seems preferable, more than one type of button class, slideshow integration, etc.
I recommend reading through the docs (http://foundation.zurb.com/docs/index.php) and if you're familiar with Skeleton you'll notice what's different.
I've used Skeleton in the past but for future projects I think I'd go with either Foundation, Columnal or Goldilocks.
The http://stacklayout.com/ is heaps better - using display:inline-block; for nestable grids means no more annoying column classes etc. It's a much nicer way to work