Zurb Foundation is one of the most advanced responsive front-end framework in the world. Take a look at their website to get familiar: Zurb Foundation CSS Framework
Foundation 4 offers a free collection of tools to create complex responsive websites easily.
It contains HTML and CSS based design templates for Grids, Buttons, Forms, UI elements, Typography and much more.
It has Flexible, efficient layout. In simple words, Zurb Foundation is what you need to start your web design carrier.