Next.js is an open-source React-based web development framework that enables developers to build server-side rendered (SSR) React applications with ease. It was created by Zeit and is now maintained by Vercel. Next.js provides a variety of features that make building React-based applications a breeze, including server-side rendering, automatic code splitting, static site generation, and more.

One of the key benefits of Next.js is its ability to provide server-side rendering out of the box. This means that your web pages can be rendered on the server before being sent to the client, providing faster page load times and better SEO. Additionally, Next.js supports automatic code splitting, enabling developers to deliver code that is optimized for each user's device and network speed.

Another feature of Next.js is static site generation (SSG), which allows you to pre-render your pages at build time. This can lead to even faster load times and better SEO, as the pre-rendered pages can be cached and served to users quickly.

Overall, Next.js is a powerful tool for building React-based applications with server-side rendering, automatic code splitting, and static site generation built-in. It is a popular choice among developers and is used by companies such as Twitch, Hulu, and Lyft.