The goal of this book is to be the best answer to the question, “If I want to learn web development with Ruby on Rails, where should I start?” By the time you finish the Ruby on Rails Tutorial, you will have all the skills you need to develop and deploy your own custom web applications with Rails.
The 960 Grid System is an effort to streamline web development workflow by providing commonly used dimensions, based on a width of 960 pixels. There are two variants: 12 and 16 columns, which can be used separately or in tandem. Read more.
Unsemantic is a fluid grid system that is the successor to the 960 Grid System. It works in a similar way, but instead of being a set number of columns, it’s entirely based on percentages.
Well you see the links click them to get more information … simple as that