Bootstrap
Bootstrap is the most popular HTML, CSS, and JS framework for developing responsive, mobile first projects on the web.
Semantic UI
Semantic empowers designers and developers by creating a shared vocabulary for UI.
Semantic UI React
Semantic UI React is the official React integration for Semantic UI. jQuery Free, Declarative API, Shorthand Props, and more.
Blueprint
Blueprint is a React UI toolkit for the web. It is optimized for building complex, data-dense web interfaces for desktop applications. If you rely heavily on mobile interactions and are looking for a mobile-first UI toolkit, this may not be for you.
NativeBase
NativeBase is a free and open source framework that enables developers to build high-quality mobile apps using React Native iOS and Android apps with a fusion of ES6. NativeBase builds a layer on top of React Native that provides you with basic set of components for mobile application development. This helps you to build world-class application experiences on native platforms.