Overview
Forged in the Dark is a tabletop roleplaying game framework and System Reference Document created by John Harper. Released in 2017, it is the underlying engine that powers Blades in the Dark and has since been used by independent designers to build countless other games, such as Scum and Villainy and Band of Blades. It excels at telling stories about capable but flawed groups of people pulling off daring missions against overwhelming odds.
The system it directly evolved from is
Description
Instead of being a single game, Forged in the Dark is an open license toolkit. Players form a crew, whether they are space smugglers, military mercenaries, or rebel outcasts, and undertake dangerous missions known as Scores. The system is heavily narrative and focuses on failing forward, meaning a bad dice roll never stalls the story, but instead introduces a new complication. It completely eliminates tedious planning phases by throwing players directly into the action.
System Overview & Key Features
The d6 Dice Pool
To resolve a risky action, a player rolls a pool of six sided dice based on their action rating. The highest single die determines the result. A six is a full success, a four or five is a partial success with a consequence, and a one to three is a bad outcome.
Position and Effect
Before the dice hit the table, the Game Master establishes the Position (Controlled, Risky, or Desperate) and the Effect (Limited, Standard, or Great). This ensures everyone understands exactly what is at stake and how much impact the action will have.
Progress Clocks
The game tracks complex threats and long term projects using circular clocks divided into segments. A stealth mission might have a clock for the guards going on high alert, filling up bit by bit as the players roll partial successes or failures.
Stress and Resistance
Characters have a Stress track that they can spend to push themselves for extra dice or to assist an ally. More importantly, players can spend Stress to resist any consequence the Game Master introduces, allowing characters to survive deadly situations by sheer willpower.
Flashbacks
Players do not need to spend hours planning a heist or mission. When they encounter an obstacle, they can simply spend Stress to declare a flashback, narrating how their character anticipated the problem and set up a solution in the past.
Phases of Play
The game flows through specific phases. Free Play is where characters gather information and choose a target. The Score is the actual mission. Finally, Downtime allows the crew to recover from injuries, reduce their heat, and work on personal projects before the cycle begins again.
Additional links
bladesinthedark.com 
https://bladesinthedark.com - Official System Reference Document and rules database
evilhat.com https://evilhat.com - Official Evil Hat Productions website