Sci-Fi: Traveller, Stars Without Number, and the Rest
Traveller for hard sci-fi merchants. Stars Without Number for sandbox explorers. Scum and Villainy for Firefly-style scoundrels.
Traveller is the original sci-fi RPG — you can die during character creation (lifepath system generates your backstory through career terms, and failed survival rolls mean starting over). Mongoose 2nd Edition is the modern standard. It excels at sandbox campaigns where the players own a ship, take jobs, and try to make the mortgage payments. Think Firefly or The Expanse.
Stars Without Number gives you sector-generation tools that work for any sci-fi system. Its faction turn system models interstellar politics between sessions. Scum and Villainy (Forged in the Dark) handles heists, smuggling runs, and criminal enterprises with a flashback mechanic that makes planning feel cinematic. For one-shots, Mothership (survival horror) and Lasers & Feelings (one-page, free) are the go-to picks.
Horror: Call of Cthulhu and Its Competitors
Call of Cthulhu is the undisputed king of investigative horror. Delta Green for modern conspiracy.
Call of Cthulhu (7th Edition) uses percentile skills and a sanity system where knowledge literally drives you mad. It's the best-supported horror RPG in existence — decades of campaigns, a vibrant convention scene, and a community that produces some of the highest-quality fan content in the hobby. The core rulebook alone can sustain years of play.
Delta Green takes the CoC engine and applies it to modern-day government conspiracies. You play federal agents covering up cosmic horrors while your personal life and sanity disintegrate. The scenario writing (Impossible Landscapes, God's Teeth) is regularly cited as some of the best RPG writing in any genre. For rules-light horror, Dread uses a Jenga tower instead of dice — when the tower falls, your character dies. It's the most intense one-shot experience in the hobby.
Universal Systems: One System, Every Genre
Savage Worlds for pulpy action. GURPS for realistic simulation. Fate for narrative-first play.
Savage Worlds is the universal system that actually runs fast at the table — exploding dice, bennies (rerolls players earn for cool moments), and a system that handles mass combat, chase scenes, and social encounters as mechanically as combat. It's the pick for groups that want to jump between genres (fantasy campaign, then a sci-fi one-shot, then weird west) without learning new rules.
GURPS is the simulationist's dream — sourcebooks researched to academic standards, point-buy character creation where you can build literally anything, and combat that models individual second-by-second actions. The Dungeon Fantasy RPG boxed set is GURPS optimized for D&D-style play. GURPS works best for DMs who love prep and players who love detail.