Pre-industrial healing is brutal. The PDF covers herbal remedies, bloodletting, surgery without anesthesia, and the creation of lye, soap, and black powder (for late TL4 campaigns).
A cold rain hammered the slate roofs of New Braintree as Wren Tolland ducked beneath an awning, the leather satchel at her hip slick with water. Inside the satchel, wrapped in oilcloth, was a relic that had become rare currency in the back alleys and campfires of the Wastes: a GURPS Low-Tech PDF, pirated and printed into a single battered codex. Its pages smelled of dust and iron, and its margins were scored with hastily scribbled notes in a dozen hands. gurps low-tech pdf
Adds deeper rules for weapon design, historical evolution of combat gear, and fortifications. Low-Tech Companion 3: Daily Life and Economics Pre-industrial healing is brutal