 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.Niven has also written a logical fantasy series "The Magic Goes Away", which utilizes an exhaustible resource called "mana" to power a rule-based "technological" magic.