Designer Summary Tome of Trade is a d20 System / OGL Product (D&D 3.5 Compatible) sourcebook It opens up the marketplace to players, to exploit or join. Within are several prestige classes for the market, along with feats, spells, items and skill uses (including a new skill) for the same. Also included is charts for creating a market, and a system for running a shop. The book can also be used with Pathfinder.