Livebook is an interactive notebook for Elixir where you write code alongside rich Markdown prose, execute it cell by cell with reactive dependency tracking, and deploy finished notebooks as standalone web applications with a single click. Nearly 6,000 GitHub stars reflect the Elixir core team's investment in a platform where code cells run on demand alongside Mermaid diagrams and KaTeX mathematical formulas. The Kino visualization library renders Vega-Lite charts, interactive data tables with sorting and pagination, Leaflet maps, and Mermaid diagrams directly within notebook output cells, while custom Kino components enable building interactive controls with sliders, text inputs, and buttons that feed values back into running code. Smart cells abstract high-level tasks into configurable UI widgets: query PostgreSQL, MySQL, SQLite, and BigQuery databases, train machine learning models with Axon, plot charts, and build map visualizations without writing boilerplate code. Real-time collaboration lets multiple users edit the same notebook simultaneously with cursor presence indicators and synchronized cell evaluation. Notebooks are stored as .livemd files, a Markdown-compatible format that renders cleanly on GitHub and integrates with standard version control workflows. Custom runtimes connect Livebook to existing Elixir applications for live introspection and documentation of running systems. The Docker image at ghcr.io/livebook-dev/livebook exposes ports 8080 and 8081 with password or token authentication. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache 2.0 licensed.