Polynote is a polyglot notebook server that enables interactive data analysis in Scala, Python, SQL, and Vega. It provides a web-based IDE with Monaco editor, real-time kernel execution, rich visualizations (Vega-Lite, Matplotlib), and tight Apache Spark integration. The architecture is a monolith: a Scala server using ZIO effects, a custom binary WebSocket protocol, and a TypeScript frontend with its own reactive state management. Key entry points are the server main class (Main.scala) and the headless notebook runner (NotebookRunner.scala). Data flows from cell edits through WebSocket messages to the kernel, which executes code and streams results back. External dependencies include JVM, Python via Jep, Spark, Coursier for dependency resolution, and various frontend libraries. While primarily an application, it also serves as a data exploration platform with streaming data abstractions and visualization capabilities.