d20 System

The d20 System is a system of game mechanics for role-playing games published in 2000 by Wizards of the Coast and based on the original Dungeons & Dragons game created by Gary Gygax and Dave Arneson. The system is named after the 20-sided die which is central to the core mechanics of the system.

Much of the d20 System was released as the System Reference Document (SRD) under the Open Game License (OGL) as open gaming content, which allows commercial and non-commercial publishers to release modifications or supplements to the system without paying for the use of the system's associated intellectual property, which is owned by Wizards of the Coast.