Material UI: Ready-to-use foundational React components, free forever. It includes Material UI, which implements Google's Material Design.

A utility-first CSS framework for rapid UI development.

Beautifully designed components that you can copy and paste into your apps. Accessible. Customizable. Open Source.

React Hooks — 👍

📋 React Hooks for form state management and validation (Web + React Native)

A completely customizable framework for building rich text editors. (Currently in beta.)

Component infrastructure and Material Design components for Angular

Authentication for the Web.

Example showing how to use NextAuth.js with Next.js

Beautiful image placeholders, without the hassle.