Wizards of the Coast has announced plans for a brand-new system license for the fourth edition of Dungeons and Dragons. As with the d20 STL for Third Edition, this is a royalty-free license that will allow third parties to publish products using the rules developed by WotC. The new system reference document will be made available early in June (just after the release of the new edition). That license only covers fantasy gaming, but a second license (the d20 GSL) will be released allowing for any type of gaming product to be developed. For analysis and follow-up on the announcement, the ENWorld boards have full details.
