D20 System

The d20 System is the rules system employed by many different companies. Much of this information comes from the Wizards of the Coast [D20 page. Please see there for more information.

History
In the eighties and nineties, rules systems were all proprietary. Only the company who owned a particular ruleset was able to take advantage of it. For this reason, there were dozens, if not hundreds, of different roleplaying games, most of which were completely incompatible with each other.

Whenever someone wanted to create a new RPG, they needed to devote half the development time to the setting, and half to creating a new system. This was a large waste of resources, as you might imagine.

The creators of the Third Edition of Dungeons & Dragons proposed an "open-source" rule system, called the d20 System. With the d20 system, anyone would be able to release an RPG with whatever setting they liked. The only system development they'd need to do would be to interpret the specifics of their setting using existing rules.

Variations
The D20 System has two main variants: known as the D20 System License and the Open Game License. This section provides a basic primer, and is not to be referenced for anyone who intends to create their own products.

Either one of these licenses permits the use of anything which is designated as Open Game Content.

D20 System Trademark License
Adherents of this license (also called the D20 Logo license) are subject to the following restrictions, as taken from the d20 System Guide:


 * Cannot contain rules or instructions of any kind that describe a process for creating a character or describe a process for applying the effects of Experience to a character
 * Cannot change or extend the definition of any defined game term.
 * Cannot include miniatures.
 * Cannot use the term “Core Book” on its cover, title, advertising, or self-reference.
 * Cannot be any form of computer or console game.
 * Must comply with quality standards as described by Wizards of the Coast and in the d20 System License.
 * A minimum of 5% of the text (word count or letter count) must be Open Game Content and must comply with the terms of the Open Game License version 1.0a.
 * Must display the d20 System Logo, or in the specific case of an ASCII text file, include the words “A d20 System Licensed Product.”
 * Must include the following text block:
 * 'd20 System' and the 'd20 System' logo are trademarks of Wizards of the Coast, Inc. and are used according to the terms of the d20 System License version 6.0. A copy of this License can be found at www.wizards.com/d20.


 * Permission is granted to translate this text into a non-English language, provided that the English text is also included, and that the translated text is identified as non-official.

Additionally, text must be included on the front or back cover which states "Requires the use of the Dungeons & Dragons Player's Handbook, Third Edition, published by Wizards of the Coast, Inc." Similar terms are also included in the Guide.

The Open Game License must be included, as well.

We have included the D20 System Trademark License for your perusal.

Open Game License
Adherents of this license are restricted only by the guidelines set forth in the Open Game License itself, reprinted here for your benefit.

Open Game Content
The core of Open Game Content is in what is termed the System Reference Document. This document provides access to all aspects of Dungeons & Dragons which are Open Game Content. For example, all aspects of the d20 rules system are permitted except character creation and experience/level gain.