Social Architecture by Pieter Hintjens was my favorite of six books read this month. A great read for anyone who works with #FOSS, it explains why community takes priority over just about anything else related to free software development, and at under 200 pages it's short!
If you are wondering how to take a pet project and grow it into a long-term asset for its users and contributors, I can't think of anything better.
One warning: the book may cause you to stop reading mid-way to put into action the ideas contained therein.