The core difference is setting and mechanical focus. Torn City is urban — crime, fighting, and city-based faction warfare. Sectorum is galactic — space navigation, commodity trading, planet colonization, and corporation warfare across 1000+ sectors.
Sectorum also adds the crew member RPG system — recruitable characters with unique skills and progression that Torn City doesn't have an equivalent of.
If you're a Torn City player who wants the same persistent-world faction drama but set against a space backdrop with trading and exploration, Sectorum is your game.