Material UI - A CSS Framework and a Set of React Components that Implement Google's Material Design
Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
Swift Bootstrap - Develop iOS apps faster
Anchor CMS - Free and lightweight blogging system
Bootstrap - Simple and flexible HTML, CSS, and JS for popular UI components and interactions
Textpattern - Textpattern is an elegant content management system that is free, open source software.