Silrin is a science-fiction RPG published by Siroz Productions. It's part of their Universom line of games (different sci-fi games sharing a common rules system), along with Whog Shrog, Berlin XVIII (first edition), and Koros.
Silrin is a small planet in the Altar solar system. Its unique continent is home to four playable sentient races: humans, Celnacks, Morkors and Keydils. Humanity is split into two factions, the city-dwelling "Fat People" (high-tech, all masculine society where political power is held by the person with the highest body mass) and the Rebels (a militaristic democracy) who live in hostile deserts.
Celnacks are humanoids indigenous to the planet. Their ruling cast is winged and their technology is primitive.
Keydils are giant rats with psychic powers who live underground, and prefer not to interact with the "topside barbarians".
Morkors are primitive apelike creatures whose tribes are in a state of constant war with the Celnacks.
The rules include a long scenario allowing the players to explore and discover the richness of Silrin.