The Starship Warden is a multi generation colony ship that has suffered a disaster,leaving its inhabitants unaware they are even on a space ship. It is the setting for the game Matamorphosis Alpha.
From the back of the first edition book:
A vast starship, a virtual world in itself, carrying colonists, livestock, and the flora and fauna of Terra is struck by a cloud of an unknown form of radiation while enroute (sp) to a distant star. Chaos reigns when the radiation kills most of the crew, and in the ensuing madness the knowledge of what the ship is and where its destination lies is lost to the survivors - and there are many survivors. Intelligent mutated animals and plants now populate the vessel, and these compete or perhaps cooperate with the humans aboard.