/usr/bin/gem RubyGems is a sophisticated package manager for the Ruby programming language. On OS X the default bindir for gems that install binaries is /Library/Ruby/bin.
/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/gem RubyGems is a sophisticated package manager for the Ruby programming language. On OS X the default bindir for gems that install binaries is /Library/Ruby/bin.
The binary is a part of Ruby public framework.