Gatsby
A React-based site generator from 2015 by Kyle Mathews. For a few years it was the way to build a fast website with React, and it drove the whole Jamstack wave.
Its signature was the GraphQL layer: all content — Markdown files, CMS entries, images, API data — was loaded into a common data graph that pages queried against. Elegant in theory, but it meant writing GraphQL to fetch a heading out of a local file, and builds slowed as projects grew. The image optimization was genuinely pioneering, though, and set a standard other frameworks have since copied. The decline came when Next.js learned static generation and did the same job without the data layer. Netlify acquired Gatsby in 2023 and the product is effectively in maintenance; new projects pick Next.js or Astro.