Four good ruby cheat Sheets:
https://overapi.com/ruby
http://www.testingeducation.org/conference/wtst3_pettichord9.pdf
https://github.com/ThibaultJanBeyer/cheatsheets/blob/master/Ruby-Cheatsheet.md#basics
https://www.vikingcodeschool.com/professional-development-with-ruby/ruby-cheat-sheet