Responsive CSS Framework Comparison: Bootstrap, Foundation, Skeleton
Bootstrap 4.0.0-alpha is a fairly large update to the framework. It has dropped Less support in favor of Sass, converted from px-based to rem-based sizing, improved its grid system, and dropped IE8 support. Also, all its JS plugins were re-written in ES6, it now uses a customized reset CSS file called Reboot, and offers flexbox support via a Sass boolean variable. In addition to this update, Bootstrap now offers themes at themes.getbootstrap.com. Also, Bootstrap will continue supporting version 3, unlike the dropping of version 2 support after the release of version 3. You can read more here. Foundation 6 is a fairly major update which includes more grid flexibility, custom breakpoints, optional flexbox, and more. Like Bootstrap 4, Flexbox is now toggleable via Sass in Foundation 6. The Sass/CSS has been reworked and consolidated, and there are fewer default styles to override on common elements. Skeleton 2 was updated in December 2014 after remaining mostly unchanged for about three years.
Related: Responsive + Fluid