Experimental bootstrap 4 theme with a 'jumbotron' example on frontpage. You can edit content of jumbotron and the 'teasers' via blocks content type on your dashboard. For editing the layout, colours and typography at this state (alpha version) you will need some basic knowledge of editing (bootstrap) css and twig. Please give it a try and file issues, wishes and comments to the github repository.
Flexcards is a bolt theme built with bootstrap 4 (alpha 6), therefore, and other reason, it is still experimental. It makes use of bootstrap 'cards' in a 'fluid container'. It is ordering the cards (or blocks) in reading direction also for desktop and tablet. But the most important point might be building the bolt menu and other parts with bootstrap css/js and use it as replacement for foundation css and js entirely (compared to the shipped base theme). Demo: choose 'flexcards' on http://try.bolt.cm **Please file issues and enhancements requests to http://www.github.com/sablonier/flexcards**