http://www.pelgranepress.com/trail/index.html Official site
Character sheet with rules summary on reverse, four sample characters, and 1920s slang.
Trail of Cthulhu is written by Ken Hite, author of GURPS Horror, Pyramid Magazine's Suppressed Transmissions column, and much more. It is a licensed homage to Chaosium's Call of Cthulhu with two great parts.
First, Trail engages the Mythos differently from Call. There is more emphasis on the unknowability of Cthulhoid creatures, most particularly in the case of the 'gods': Cthulhu, Hastur, Azathoth, all the rest are presented with no statistics except the Sanity and Stability loss they cause (more about that later). Instead, each big Mythos beastie is described in half a dozen or more key ideas which may or may not contradict each other.
This is a great aid for Keepers (GMs) who want to keep players off balance. Are we up against a cosmic force, a powerful alien who can crush us, or the ideology of a cult? Are cultists deluded about the nature of their deity? Or will the Keepr play Cthulhu as the sentient force of gravity this adventure, and as the telepathy-made-flesh icon of the Deep Ones next time?
Shub-Niggurath is a cosmic principle, an Outer God of anti-entropy, or perhaps of proto-entropy. Not of order, but of creation and drive to exist, to differentiate something from the hydrogen soup that is everything.
“Shub-Niggurath” is the symbolic term for the act of miscegenation among the various species and Great Old Ones. The lore of Shub-Niggurath is nothing more than alien genetic manipulation, expressed in magical and ritual terms by confused cultists.
The other pillar supporting Trail of Cthulhu is the GUMSHOE rules system, created by Robin Laws of Feng Shui, Robin's Laws, Vampire and Earthdawn material, and much more. It is an "Indie" kind of resource management system focused on supporting the particular genre of investigative horror. Clues, in this system, should not be discovered by a random die roll --the result of a Spot check or Library Use roll-- but come automatically to characters with the right skills. "House" never worries about the lab tests coming back; you worry about how to interpret them.
Similarly, in Trail, core clues are automatic; supplementary clues are gained by spending points from your investigative abilities: 1 for a clue or benefit, 2 for a big clue or benefit. "Investigative spends" are also good for player input in the game: bringing on a flashback, introducing a contact, revealing undisclosed (and previously non-existant) background. Points spent are thus "spotlight points" for each character to shine and contribute.
Random resolution is kept for fun things like running away from monsters, shooting monsters, and passing Stability tests. The mechanic is a d6 rolled against a difficulty, typically 4. Players spend points from their General abilities to add to the roll and beat the difficulty. This means that as the adventure goes on, point pools run low and the tension builds.
I've mentioned Stability twice now. One further refinement or re-presentation of Call of Cthulhu is a split between Stability and Sanity. Stability goes up and down as characters witness horrors (or commit them) and have time recuperating with their wives, dogs, therapists, or stamp collections. A convensionally insane person has low or negative Stability. Sanity, on the other hand, pretty much only goes down and stays down as characters are exposed to the Mythos. A character may thus have low Sanity and high Stability: great knowledge of the horrors beyond the day-to-day world, but stiff resolve and high functionality for the time being.
The rulebook (creepily illustrated by Jérôme Huguenin) has conversion notes for Call of Cthulhu's Basic Roleplaying rules, and scenario notes are going up on Pelgrane Press's site. I am finding the more contemporary rules very congenial and greatly enjoy running classic Call of Cthulhu scenarios with Trail.
Problems with the game: My main complaint is First-Edition-itis. Some rules are scattered across two or three sections: firearms for combat, sanity and insanity, modifiers for various actions. Second, Mythos magic is written up for human beings and requires (minimal) patching for use with monsters. The publishers promise this will be addressed in a supplement.