Our current book is "A Philosophy of Software Design," by Stanford professor John Ousterhout. Ousterhout noted that computer science courses often teach theoretical computer science or specific technologies, but rarely explicitly tackle software design. He decided to offer a class on design, and this thin volume (less than 200 pages) is based on the first few years of teaching the class.
We are currently discussing the first half of the book (chapters 1-10), as well as software design in general, on Thursday 13 September, at lunchtime.
As far as I can tell, this book is available only in paperback, and only from Amazon. It's pretty cheap, though. https://www.amazon.com/Philosophy-Software-Design-John-Ousterhout/dp/1732102201/