[RMPR]

I wonder why

Free as in freedom, Sam Williams

Wasn't mentioned (maybe it's too recent?), the book is written as biographical snapshots of Richard Stallman, basically the story of the Free software, I think it's a great complement for The Cathedral and the Bazaar which was already mentioned.

[RMPR]

Something I also liked as far as history is concerned: https://news.ycombinator.com/item?id=20797521 while it's not a formal book, it covers the motivation and some nitty gritty stuff you might find useful.