Jekyll is a mature, blog-aware static site generator written in Ruby. It transforms plain text files (Markdown, Liquid templates, HTML, Sass, CoffeeScript) into static websites, supporting collections, posts, drafts, data files, gem-based themes, and a rich plugin system. The architecture is a monolith library with a CLI interface (build, serve, new, clean, doctor, new-theme) and a built-in development server with LiveReload. Key data flows: source files are read by a Reader, processed through converters (Markdown via Kramdown, SmartyPants, etc.), rendered with Liquid templates and layouts, and written to a destination directory. Incremental builds are supported via a regenerator that tracks file modifications and dependencies. The codebase is well-structured with extensive unit and integration tests (Minitest, Cucumber), benchmarks, and profiling tools. It demonstrates strong engineering practices: a plugin architecture with hooks, converters, generators, tags, and filters; a drop-based Liquid integration; caching; and platform-aware utilities. The project is actively maintained with frequent releases, a formal release process, and community governance.