Trail of Cthulhu
Trail of Cthulhu is an attempt to remake Call of Cthulhu for a younger audience by Kenneth Hite and Robin D. Laws (who devised the GUMSHOE system.) There is a strong emphasis on investigation and sanity built into the system, with other mechanics such as combat heavily streamlined and simplified. Trail is set in the world of the Cthulhu Mythos of H.P. Lovecraft, but the publisher produces other settings using the same system, such as Esoterrorists and Fear Itself.
Roll 1d6 against a target number. Skills consist of pools of points that can be spent before each roll or add to the roll, but once used these are gone until the character rests. It is one of the most simple skill/combat systems on the market.
If a player enters a location where a clue can be found, he needs only declare that he is using an investigative ability, such as Library Use or Forensics. If a clue is vital to the plot then he finds it automatically simply by using the correct ability. If a clue is not vital but merely useful, he can spend points from his skill pool to obtain it; these points do not refresh until the end of the adventure.
Chargen operates on a simple point buy method. Skills that form part of your occupation are bought at a rate of 1 for 2. Sanity, Stability, and Health are bought in the same way as skills. Credit rating plays a major role in the game by determining which social strata of society you can comfortably interact with.
For every few points of Stability or Sanity, you choose a loved one (or in the case of Sanity, a treasured belief) that keeps you sane. If these are threatened you risk losing those points. Each investigator also has a Drive, a motive such as Curiosity or Revenge for getting mixed up in nightmarish and dangerous situations that a more sensible person would avoid. The Keeper can use this to prod you into investigating things that would be better left alone.
Similar to CoC, gameplay consists principally of following a trail of clues and trying to survive confrontations with the dark forces arrayed against you. The game presents both a 'Purist' and a 'Pulp' game style. The 'Purist' game-type focuses on a bleaker Mythos, where the pursuit of the truth dooms both the investigator and innocent bystanders with an unpreventable horror and is geared towards a more traditional gameplay. The 'Pulp' game-type intends for the intrepid investigators to have a fighting chance against the Mythos. The concepts are later used in the book to allow certain rules to be added or excluded to achieve whatever feel The Keeper is aiming for. Of course, one can also try to achieve a balance between the two styles of play.
SAN is divided into two traits, Sanity, and Stability. Sanity represents how much you know about the awful truth and the pointlessness of human existence; Stability represents how freaked out you are right now. Horrible mundane experiences reduce Stability but not Sanity.
When a player loses his mind in ToC he is not told what form of madness he has. Instead, he is sent out of the room and the Keeper and other players confer, and then act to recreate his madness through roleplay and meta-play. For example, if a character becomes afflicted with paranoia, the Keeper may ask the players to give him funny looks, snicker, pass notes to the Keeper and whisper to one another, saying 'nothing' when the afflicted player asks what's up.