From the introduction: Modulus is a human-oriented, gritty, setting-agnostic role-playing system! Math is kept to a minimum, and the rules absolutely needed for play fit on the back cover. The book contains a generic role-playing system with Game Master commentaries on all rule sections to provide insight into how to run the game, as well as why certain rules were included. The generic system includes two variants right in the text which allow your campaigns to have a gritty feel or lighter tone. Then, there is a complete, though brief, Game Master section covering how to build settings, write adventures, and run sessions in Modulus, with work sheets for each activity included in the appendix. As if that was not enough, the book also contains two separate setting supplements, showing how the rules can be used to flavor a setting or altered to fit the needs of the table. Use these supplements as a starting-point, or in their entirety. Low fantasy and hard sci-fi are included, with additional setting support modules planned for the future.