An "Open" Gaming System created by Wizards of the Coast (WotC) to support their line of Role Playing Games after they aquired TSR.

The name itself is slightly misleading if you are expecting West End Games' (WEG) d6 system translated to a d20 (This comes from that fact that the system was announced shortly after WotC aquired the rights to the Star Wars RPG from WEG). While the d6 system works soley on six-sided dice in multiples to produce stats, the d20 system uses the same set of polyhedral dice that Dungeons & Dragons did. The diffrence being that most checks are made using a d20 +/- modifiers. This makes the d20, after character creation, the most used die in the game.

Why Open is in quotes:
Originally the d20 system itself was supposed to be an open gaming system, the rules were to be available so that any game comapny could publish supplements against it. No progress has been made towards this recently, probally because they have yet to publish any standalone d20 products. It also is not turely open since it requires some lincecing agreements which restrict certian aspects of the system, such as character creation.

Current d20 Games:

I have to disagree with the writer of the previous writeup. The d20 system is most certainly open. The restrictions that they place upon it are a lot less harsh than some open source licenses.

The restriction is only on putting the d20 logo in your product. If you wish to use any material that has been released as "Open Gaming Content" then you need not do anything at all. You just may not put the d20 logo anywhere in your product. In addition, you may not put any sort of trademark of Wizards of the Coast in your product, as well. (A company needs to "OK" something that actually uses their trademarked names).

So, feel free to go out and make a game which uses the entire d20 system. But, if you want to call it a "d20 game" you must not break any of the restrictions. These include small things like "Include this license with your game, so that other people may derive from YOUR work" and the one that I have a problem with "Do not cover things such as character generation" (Which is WotC's method of selling the core rulebooks which are the only things that may detail those pieces of game info.)

There have been a lot of new d20 games released recently. A super hero game, a swashbuckling game, a lot of game conversions including an official Call of Cthulhu conversion, and a lot of others. What I find exciting is that they are releasing a lot of modules for D&D that are d20 -- so WotC doesn't even have to approve them. This includes the Adventurer's Keep modules by Alderac Entertainment Group. (Cannot find a better price -- $2.50 for a complete module.)

For more information regarding what the d20 license does and does not cover, please check the "d20 system reference document", better known as "The SRD" ( The open gaming foundation also hosts another game which is COMPLETELY open called "Dominion." (I've glanced at it, and it also looks nice.) Also, wizards has some information about it available at,3 (which may change soon, knowing how often Wizards will change the URL of their webpages.)

The d20 System has several design strengths over earlier gaming systems, which make the game easier to play. They are:

Roll high
Whenever a player is rolling a die to do anything, they always want to roll high. There are no good effects to be gained by rolling low. Ever.
Higher is better
For any ability or statistic that a player has, they always want a high number. Gone are the days of trying to minimize your THAC0 and AC while increasing your hit points.
Positive is good
Notice a trend yet? Anything which modifies a number is good if it is positive, and bad if it is negative.
Use of formulas
Instead of using lookup tables for finding values, almost any value is derivable from a simple (usually linear) formula (the one exception to this seems to be max carry weight).
Precomputability of modifiers
Most modifiers can be easily precomputed, such that a player rolls a die, adds their combined modifier, and checks to see if the roll was high enough to be successful.

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