Build Awesome Command-Line Applications in Ruby 2
David Copeland
Poolology - Mastering the Art of Aiming
Brian Crist
The Well-Grounded Rubyist, Second Edition
David A. Black
Exploding Rails
Ryan Bigg
Practical Object-oriented Design in Ruby
Sandi Metz
Clean Code
Robert C. Martin
Continuous Delivery
Jez Humble & David Farley
Growing Object-Oriented Software, Guided by Tests
Steve Freeman & Nat Pryce
Refactoring
Jay Fields & Shane Harvie & Martin Fowler & Kent Beck