Which version(s) of Mac OS X have Ruby installed by default?
10.14   ruby 2.3.7p456 (2018-03-28 revision 63024) [universal.x86_64-darwin18]
10.13   ruby 2.3.3p222 (2016-11-21 revision 56859) [universal.x86_64-darwin17]
10.12   ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]    
10.11.2 ruby 2.0.0p645 (2015-04-13 revision 50299) [universal.x86_64-darwin15]
10.10.2 ruby 2.0.0p481 (2014-04-08 revision 45883) [universal.x86_64-darwin14]
10.9.0: ruby 2.0.0p247 (2013-06-27 revision 41674) [universal.x86_64-darwin13]
10.8.5: ruby 1.8.7     (2012-02-08 patchlevel 358) [universal-darwin12.0]
10.7.5: ruby 1.8.7     (2010-01-10 patchlevel 249) [universal-darwin11.0]