Known Space
Many of Niven's stories—sometimes called the Tales of Known Space—take place in his Known Space universe, in which humanity shares the several habitable star systems nearest to the Sun with over a dozen alien species, including the aggressive feline Kzinti and the very intelligent but cowardly Pierson's Puppeteers, which are frequently central characters. The "Ringworld" series is part of the Tales of Known Space, and Niven has shared the setting with other writers since a 1988 anthology, "The Man-Kzin Wars" (Baen Books, jointly edited with Jerry Pournelle and Dean Ing). There have been several volumes of short stories and novellas.