Bootstrap 4 drops IE9 support and goes full flexbox
For everyone saying "Foundation" when people ask what else... let me explain why Bootstrap is used so much more frequently than all other options combined.http://foundation.zurb.com
vs
http://getbootstrap.comEach has a link to 'download'.Foundation's link takes me to a page where I have a bunch of options, and a bit "build a custom generated version".Bootstrap's takes me to a screen with 3 options, but also - and this is key - CDN links.  Right there.  I can paste a few lines in my HTML template and start working.I don't need to download/generate code.I don't need to install node/npm/etc.I don't need to install and learn sass stuff.I don't need to make a lot of decisions or do a lot of extra unrelated stuff to get started.Bootstrap is the PHP of the css/grid/framework world (for better and for worse).I truly hope they keep the CDN hosted stuff for Bootstrap 4.EDIT: didn't mean to pick on foundation specifically - this "take control of every aspect of all your layout/grid/css" that most other frameworks require works to their disadvantage when it comes to popularity and uptake.