The GUMSHOE System is a role-playing ruleset created by Robin Laws in 2007 for running investigative scenarios, used in various games published by Pelgrane Press. Trail of Cthulhu won the 2010 Lucca Games award for best role-playing game, and following the Hillfolk Kickstarter its SRD was released under both the Open Game License and Creative Commons Attribution.
It starts from one problem: in most systems, a failed roll can cost the players a vital clue and grind the scenario to a halt. GUMSHOE turns this around by making investigative abilities always work. If a scene contains a core clue and a character uses a relevant investigative ability, the clue is found — no dice involved. Spending ability points yields extra clues that help but are not required.
Dice appear only where an uncertain outcome is dramatically appropriate: a general-ability test is one six-sided die against a standard difficulty of 4. There are no levels, and rolling is kept in the players’ hands wherever possible. The tension moves from “can we find it?” to “what does what we found mean?”