The Prepless GameMaster (2020)

Publisher's blurb:

The Prepless Gamemaster is a complete system for playing RPGs without any prepwork.
You can just sit down and start playing whenever, wherever.

The tools of The Prepless Gamemaster will help you to effortlessly deal with the unexpected in a way that is exciting and drives the story forward. If you like preparing your games, the prepless GM will allow you to better deal with situations where players do not follow your carefully laid plans.

I know some GMs believe that you must always spend at least some time preparing for every game. But I’ve been running completely prepless games for over 20 years. And every time I came across a challenge – whether it was running a riddle, murder mystery, or even an escape room – I created a tool for running that story without any prep. The Prepless GM is the culmination of 20+ years of playtesting tools that will help any GM run a game on the fly.