answer:Much of the D20 system was released under an open license so not really. All they really have a legal claim to is the stuff that they made themselves that isn’t covered by that license, like storyline stuff. As for mechanics, if they took it to court then they would lose as soon as the defense lawyer whipped out a copy of the licenses that WOTC themselves wrote. However, they realized that the license for AD&D 3/3.5 was not in their best interests and revised it for 4th edition, but as far as the old D20 used in 3/3.5 goes, they can’t say a damn thing about it since they painted themselves into a corner with the original OGL.