Traveller uses a
2d6 dice system where characters add their
relevant characteristic and skill levels, with various possible
target numbers and situational modifiers. It also has a notion of
“task chains”, where one roll gives a bonus or a penalty to
another. This post runs through all these variations, with lots of
This is a homebrew skill I gave one of my Masks of Nyarlathotep players after they decided to become friendly with a time-traveller. 10% chance of answering a plot-relevant question, and immediate recognition of key NPCs.
Call of Cthulhu uses a roll-under percentile dice system. It also has a notion of task difficulty and situational modifiers, and a way for two characters to directly compete. This post runs through all these variations, with lots of graphs, and gives my rules for deciding what sort of roll to make when.