Display orphan gems (those that are not depended upon).

gistfile1.rbx

#!/usr/bin/env ruby
gems = {}
`gem dependency -R`.split("\n\n").each do |gem|
  unless gem["Used by"]
    version = gem[/\d+\.\d+\.\d+$/]
    name = gem[4..-1][/^.*(?=-\d\.)/]
    (gems[name] ||= []) << version
  end
end

gems.sort_by { |n,v| n.downcase }.each do |name, versions|
  puts "#{name} (#{versions.join(", ")})\n"
end