Derivative 14 is an an expansion for FIST that enhances the espionage procedural feeling of the core game.
The PDF is 16 pages, with a strong, sleek, technical military vibe. It matches the energy of the core book almost perfectly---although there is one photo of a raccoon that feels a little goofy.
Derivative 14's biggest addition to FIST is a small change to the core game loop. When deploying on a mission, the operatives roll for tasks like reconnaissance. The rolls influence the mission by giving the operatives more resources, better information, or creating new complications. It's a neat mechanic and feels very Blades In The Dark, and it doesn't require a lot of mental overhead from the GM, players, or the underlying math of the system.
Derivative 14's other major component is new Roles and Traits. They're all flavorful and weird, with a standout being the Figment, who is a PC that is actively being dreamed to life by someone else. There's also a set of Traits for playing as animals, in case you perhaps want to steer in a We3 direction.
Finally, Derivative 14 introduces Complications, which are like negative Roles that you can lean into to gain more War Dice. It's a nice way of centering the characters and their decisions over "winning" the mission, and I'd strongly recommend adding this to your game even if you leave the rest of Derivative 14 on the table.
Overall, Derivative 14 is an excellent, well-crafted, and surprisingly subtle add-on that enhances FIST's core gameplay without significantly disrupting anything.