The Boundless Society Dossier is a faction pack for FIST that introduces several mad-science themed antagonists.
The PDF is 4 pages with a plain layout that makes it feel like it could be a document from FIST's setting.
Contents-wise, the writing here is extremely strong and does a great job of establishing character and threat for each of the included antagonists. Stats are not provided, but in some ways this is better. There's some degree of ambiguity in the entries, and specific stats would dispel that completely.
Overall, if you want some new antagonists to build FIST missions or campaigns around, this is a great asset.