Office UI Fabric React is the official open-source React front-end framework designed to build experiences that fit seamlessly into a broad range of Microsoft products. Use this tag when your question is specifically around the ReactJS usage of the Office UI Fabric.

Office UI Fabric React is the official open-source React front-end framework designed to build experiences that fit seamlessly into a broad range of Microsoft products. It provides robust, up-to-date, accessible components which are highly customizable using CSS-in-JS.

Office UI Fabric React is the preferred framework of the for building custom applications that fit into the Microsoft Office ecosystem.

for more details, https://github.com/OfficeDev/office-ui-fabric-react
see also