sunnypilot is a community fork of comma.ai's openpilot, an open-source driver assistance system (ADAS) designed for real-time operation on dedicated hardware (comma three/4, panda). The codebase implements the full autonomy stack: camera and radar perception, path planning, longitudinal/lateral control, driver monitoring, and localization via Kalman filters. It runs as a set of daemon processes orchestrated by a process manager, communicating through a shared-memory pub/sub messaging layer (msgq) with Cap'n Proto serialization. The system includes a full-featured Raylib-based UI with on-road HUD, settings panels, and an installer, plus cloud connectivity through Athena (remote commands, registration) and the fork-specific Sunnylink (settings backup/restore, telemetry). Beyond the core openpilot functionality, sunnypilot adds numerous extended features: Modular Assistive Driving System (MADS) for configurable steering modes, neural network lateral control (NNLC), map-based speed limit assist using OpenStreetMap data (mapd), intelligent cruise button management, dynamic experimental control, and a model manager that fetches and caches driving model bundles from a remote manifest. The fork maintains its own cereal schema extensions and custom UI layouts for both touch (mici) and big-screen (tizi) hardware variants. The repository includes extensive testing infrastructure: unit tests for most modules, process replay tests that compare outputs against reference logs, longitudinal/lateral maneuver simulations, and CAN bus analysis tools (cabana, replay). It also provides simulation bridges (MetaDrive, joystick) for closed-loop testing. The build system uses SCons for C++ components and uv for Python dependencies, with CI pipelines for model building, release drafting, and route uploads.