RubberDucky is a responsive mobile first CSS framework that utilizes the 12 column grid. Based off of simplegrid, RubberDucky's grid is easy to learn and offers simple, flat, minimalist styles to components. Unlike other frameworks, RubberDucky only has a few class that you need to learn to get your website up and running, making it a great framework for beginners or lightweight projects.
Follow the link to read the documentation.