Mistaken is a FIST hack where the PCs play as members of CYCLOPS.
The PDF is 16 pages with a wonderful, evocative cover and a generally clean layout. The text feels slightly cramped in a few places, but the overall structure is easy to read.
Contents-wise, this is a fairly comprehensive hack of FIST's rules. CROs are stronger but more limited than FIST agents, and have to worry about HUMANITY, DESPAIR, and other factors that FIST is relatively free from.
There's some sample missions included, as well as rules for collaboratively worldbuilding a mission zero that went poorly before the game began.
The writing is direct and evocative, and the overall game environment is interesting. The sample missions are super flavorful, and there's plenty of room for them to go wrong.
Overall, this is a solid examination of an under-examined faction in FIST, and potentially also a good system for running something like a Bad Batch game, or just a more bleak examination of spycraft. Pick it up if you like FIST but want something a bit darker in tone.