Semantic is a UI component framework based around useful principles from natural language.

Material UI: Comprehensive React component library that implements Google's Material Design. Free forever.

An enterprise-class UI design language and React UI library

Flat UI Free - Design Framework (html/css3/less/js). Flat UI is based on Bootstrap, a comfortable, responsive, and functional framework that simplifies the development of websites.

The official Semantic-UI-React integration

Fluent UI web represents a collection of utilities, React components, and web components for building web applications.