Programming Scala is an excellent open source book that used to be distributed under O’Reilly’s Open Feedback Publishing System (OFPS), a platform which offered public commenting on digital manuscripts. Sadly that system was retired by O’Reilly.
Many of the book projects from OFPS were migrated to O’Reilly’s Atlas Reader. Sadly, Programming Scala was not migrated. But given the book is such a useful read and is published under an open source license, I can share the book here.