An early science fiction RPG, the Yolmi were an evil alien race that the human PCs encountered far too often for their tastes. A level/class-based game, it includes the usual character rules as well as spaceship rules and a respectably large bestiary.
From Heroic Worlds:
Science-fiction system with D&D-derived class-and-level rules that covers human characters on a future Earth (soldiers, cyborgs, scientists, and psychics), their skills, experience, equipment, et al. Combat includes both futuristic weaponry and unarmed fighting. The background material covers space travel, galactic trade, alien races (including the evil Yolmi), over 140 creatures, plus starship statistics and combat rules. What a title - Realm of Yolmi - just kind of rolls right off the tongue, doesn't it?
659-010.1/954-77. 116 pp. West Coast Games, 1977 (1st ed.).
659-010.1/060-78. 180 pp. Avant-Garde Simulations Perspectives (ASP), 1978 (2nd ed.).