Since even before Fallout 3 was released, a rumor of a Fallout MMO being in the works was already circulating around the web. To keep things brief, the MMO is supposedly a real thing and is in the works, but Bethesda has been intent on trying to delay or outright stop development on the title. While there was a recent preliminary injunction against Interplay for the project, a recent appeal from Bethesda has been denied. So for the time being, the developer may continue working on the MMO.
Whether an actual product will come out of Interplay remains to be seen, but for now it is free to continue its development.
[Source via Joystiq]