Full Article here (on MySQL, then D&D)D&D “version 4.0” will soon be released, and many game beta testers believe the system has been radically overhauled and improved. However, this new system will not be released under the OGL. It will however, be released under the “Dungeons and Dragons 4th Edition Game System License” (GSL).
The GSL license has not yet been made public, but there are rumors, speculations, and concerns, fueled by online posts made by the brand manager and licensing manager for Dungeons and Dragons, and relayed by the lead writer of third-party publisher Necromancer Games that the GSL will contain a “poison pill” clause – that is, in order to use the GSL, a game company must not publish anything under the OGL.
This would be like Microsoft saying that developers for Windows Vista are forbidden from publishing anything under the GNU public license. And the upshot is now that developers have to choose between not developing games with the improved system or destroying their back-catalogs.