Gutenberg is WordPress’s new default page builder
It now comes included with WordPress 5.0 which was released today.
According to WordPress – “We’ve made some big upgrades to the editor. Our new block-based editor is the first step toward an exciting new future with a streamlined editing experience across your site. You’ll have more flexibility with how content is displayed, whether you are building your first site, revamping your blog, or write code for a living.”