GatsbyJS is a free and open-source static site generator based on React. It uses a modern development stack including Webpack, GraphQL, and modern JavaScript and CSS frameworks. It also provides a rich set of plugins, starters, and themes.
ESLint is a linter for JavaScript that analyzes code to detect and report on potential problems and errors, as well as enforce consistent code style and best practices, helping developers to write cleaner, more maintainable code.