PolyCast turns a JSON script into a low-poly 3D podcast video. Two characters banter in a studio, voices come from Cartesia or your computer's free built-in voice, lip-sync runs off the real audio, and camera cuts and captions are cued to the exact word. It renders frame by frame with Three.js in headless Chrome, and it also works as a Claude Code skill: describe a video, get the MP4. Free and MIT licensed.