React-Bootstrap is a library of reuseable front-end components. You'll get the look-and-feel of Bootstrap, but with much cleaner code, via React.js framework.
Radium is a set of tools to manage inline styles on React elements. It gives you powerful styling capabilities without CSS.
FixedDataTable is a React component for building and presenting data in a flexible, powerful way. It supports standard table features, like headers, columns, rows, header groupings, and both fixed-position and scrolling columns.
Elemental UI is a flexible and beautiful UI Toolkit for React.js Websites and Apps.
There are modular set of UI scaffolding components and controls for React that are built from the outset to natively implement React patterns.
Draft.js is a framework for building rich text editors in React, powered by an immutable model and abstracting over cross-browser differences.