According to this, Cinemagraphix Entertainment is sueing 3D Realms for copyright infringement over a project called Earth No More.
Apparently, Cinemagraphix shopped an idea around in 2005 for sci-fi game called Earth No More, 3D Realms being one of the companies to see the presentation. The Duke Nukem Forever developer then announced a sci-fi game called Earth No More in June 2007.
Cinemagraphix doesn’t think this is coincidence. In January the company filed for damages, including $150,000 and a share of the game’s profits. The claim is that 3D Realms not only stole pinched the name, but the premise and concept art as well.