[jjjjjosh]

Hands-down, Practical Object-Oriented Design in Ruby (http://www.poodr.com/) - some of it I don't agree with but it's all wonderfully put-together: clear and concise, with wonderful examples. Much more about OO design than Ruby, non-Rubyists will get 98% of the value out of it that Rubyists would.

[censhin]

I'm glad to see someone posted this book. I think it's far undervalued. Definitely a must read. The Ruby written could be completely replaced by pseudo code, and it wouldn't change the lessons taught.

[rimliu]

And there is another book by Sandi, released this year. https://www.sandimetz.com/99bottles/

Her books and her talks had the biggest influence on me regarding code design. At least influenced to think a lot more about it.