gets medieval.
From Arkenstone Publishing
PDF – Pay What You Want
The ancient game of Dungeons & Dragons is played for victory. We play to improve and learn. There is no fairness of sport, nor soporific of power fantasy, merely the earnest exploration of the possible and the fantastic.
Muster is a friendly introduction to the particular ethos and technique of playing D&D as a wargame, a kriegsspiel. It's for both players and referees interested in learning about this distinct approach to the game. For best results, study Muster alongside the old school D&D rules text of your choice.
The book is free, and free to share, CC-licensed. Hopefully, it'll be useful for both new and advanced gamers in thinking about the hobby!