Doctors Without Borders (MSF) has their publications on line for free as PDFs; Their Clinical Guidelines-Diagnosis and Treatment Manual is also available as an iPhone and Android app:

https://medicalguidelines.msf.org/viewport/MG/en/guidelines-16681097.html

Also available at no charge are their clinical guidelines for obstetric and newborn care, essential drugs, TB, cholera, measles, and public health engineering (need to set up clean water, sanitation for 20,000?)