Old-School Essentials: Adaptation Guidelines [PDF]
The old-school gaming scene is sitting on a secret: a huge number of games, despite having different brand names on their covers, are highly compatible! This cross-compatibility between many games means that a great wealth of adventures, campaign settings, and rules supplements can be used with Old-School Essentials.
Old-School Essentials is 100% compatible with the 1981 edition of the world’s most popular fantasy RPG, commonly known as the Basic/Expert edition (B/X for short). Any material published for the Basic/Expert rules can be used directly with Old-School Essentials. Decades of adventure are at your fingertips!
This document provides notes on how some other popular old-school games vary from the Basic/Expert rules.