Bootstrap is the more common of the two in our index: it runs on 9,564 websites against 856 for ZURB Foundation, and 98 sites use both. Counts come from real scans, not vendor claims.
Bootstrap is a free and open-source CSS framework directed at responsive, mobile-first front-end web development. It contains CSS and JavaScript-based design templates for typography, forms, buttons, navigation, and other interface components.
Zurb Foundation is used to prototype in the browser. Allows rapid creation of websites or applications while leveraging mobile and responsive technology. The front end framework is the collection of HTML, CSS, and Javascript containing design patterns.
98 sites run both Bootstrap and ZURB Foundation. That is 11% of the sites using ZURB Foundation, the smaller of the two.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.