Collabook is a free, open-source collaborative RPG with an AI Dungeon Master that reacts dynamically to your choices. Each adventure has a time limit — survive the challenges before the clock runs out. Play solo or cross paths with other players in the same world. When your story ends, download it as a PDF to keep forever. Privacy-first, no paywalls, no real names required. Three worlds: Medieval, Epic Fantasy, Sci-Fi.