Overview
Released in 2014 by Chaosium, Call of Cthulhu 7th Edition is the latest version of the cult-classic cosmic eldritch horror role-playing system originally launched in 1981. The story is based off of the literary works of H.P. Lovecraft and
lovecraftian works. Instead of setting the players up as heroes, the characters are regular investigators who are exploring cults, forbidden knowledge and various eldritch-cosmic entitites and threats.
Description
Occupations in the game for the characters include academics, reporters, and private investigators. The gameplay loop revolves around uncovering information, analyzing clues, and evading dangers. As the supernatural elements in the game are considered more powerful than the investigators, they have are not expected to actually confront most of the threats head on. Instead they usually have to resort to avoiding or escaping any situation that may arise. Combat is lethal and usually leads to characters getting permanently killed or pushed to insanity (which eventually is the same).
System Overview & Key Features
Percentile Framework (d100)
Every action is resolved by rolling two ten-sided (d10) dice to get a result from 1 to 100. If you roll is equal to or under your skill rating, the action is deemed a success. This approach simplifies the mechanical process of the game, as there are no complex tables to keep track of and compare to decypher whether it is a success or failure.
Pushed Rolls
If a character fails a skill check, they may attempt to "push" the roll, allowing for a second attempt. This requires the player to come up with a new, more desperate approach to performing the task. If this subsequent pushed roll also fails, the Keeper describes a severe and immediate negative consequence.
Sanity and Madness
A core mechanic of the system is the tracking of mental stability. Investigators lose points from their Sanity gauge when exposed to anomalous creatures or disturbing truths. Drops in Sanity result in the character experiencing temporary or permanent forms of madness, which can manifest as new phobias, delusions, or a temporary loss of player agency over the character.
Bonus and Penalty Dice
To account for situational advantages or disadvantages, the game employs a system of bonus and penalty dice. If a character possesses a distinct advantage when performing a task, an extra d10 is rolled and taking the higher result. A disadvantage means rolling an extra d10 and taking the lower result.
Combat Lethality
Physical altercations are inherently dangerous by design. Investigators possess limited hit points, and the damage output of both conventional firearms and anomalous entities is high. Recovery mechanics are slow, simulating realistic healing times. This structural lethality serves to discourage combat and incentivize stealth and investigation.
Expendable Luck
Players can spend points from their character's Luck pool to retroactively lower a dice roll. The points are subtracted on a one-to-one basis until the dice result qualifies as a success. This ensures that the Luck pool is a limited resource which should be used and utilized in the most critical situations.
Additional links
chaosium.com 
https://chaosium.com - Official publisher website and digital storefront
drivethrurpg.com https://drivethrurpg.com/browse/pub/2/Chaosium - Digital repository for official scenarios and sourcebooks