Foundation - It also has a mobile-first grid system and many components that are missing from Bootstrap. Take a look at Foundation's responsive images, Equalizer, Pricing tables, Switches and JoyRide for some features you won't find in Bootstrap. It's easy to customize Foundation based sites using a separate style sheet or SASS. Foundation uses em sizing for most elements (ie: grid column widths, media queries, font-sizing, etc..) which provides improved flexibility over Bootstrap's percentage based unit sizing.