GUMSHOE is a simple, skill-based system which uses d6 dice. It was devised specifically for investigative games, because it sports an extended list of investigative abilities from laboratory forensics to questioning people. To gain a vital clue from a scene, players just need to activate one of their investigative abilities to get it. This does away with a traditional problem of investigative games - when players got stuck because of some bad rolls and didn't pick up on an important clue.
Since it has a System Reference Document, anybody can publish their own material for the game (with some minor restrictions).
GUMSHOE has a bunch of settings published for it. Many of them include additional rules to expand your options.
- Ashen Stars: the sci-fi setting. Has rules for space combat, aliens, etc.
- Cthulhu Confidential: eldritch horror+noir. Includes rules for solo play.
- Esoterrorists: the first setting published for GUMSHOE. Has an enhanced edition out for
- The Fall of Delta Green: A horrific black ops campaign in the 1960s.
- Fear Itself: personal horror game. Adds psychic powers to the rules. Has a 2nd Edition out.
- The Gaean Reach: Vancian science fiction setting.
- Lorefinder: adds GUMSHOE's investigation rules to Pathfinder.
- Mutant City Blues: Cop Drama+Supers. Adds rules for super powers and the investigation thereof.
- Night's Black Agents: Super spies vs Vampires! Features expanded rules for combat and action sequences, as well as plenty of bloodsucker types.
- Swords of the Serpentine: the swords-and-sorcery setting. Bunch of new rules for the fantasy genre, particularly for magic & combat.
- TimeWatch: Time travel!
- Trail of Cthulhu: Pretty self-explanatory.
- The Yellow King: A multi-setting campaign of horror in which PCs in subsequent settings are mysteriously connected. New rules for player-facing combat and injury (mental as well as physical).
- Bubblegumshoe: published under the GUMSHOE OGL, emulates the teen detective genre with rules for social ties.