server&client.rb

#server
require 'drb'

class Calculator
  def add(a, b)
    a + b
  end
end

calculator = Calculator.new
DRb.start_service('druby://localhost:12345', calculator)
DRb.thread.join


#client
require 'drb'

DRb.start_service
calculator = DRbObject.new_with_uri('druby://localhost:12345')

result = calculator.add(5, 3)
puts "Result of remote addition: #{result}"