Using the server2.rb as the server for the 2 clients does not yield parallelism.

server2.rb

require 'celluloid/zmq'
require 'colorize'
Celluloid::ZMQ.init

class Server
  include Celluloid::ZMQ

  def initialize()
    @socket = Socket::Pull.new

    begin
      @socket.bind('tcp://192.168.1.10:3435')
    rescue IOError
      @socket.close
      raise
    end
  end

  def run
    loop { async.handle_message @socket.read }
  end

  def handle_message(message)
    DisplayMessage.message(message)
  end
end

class DisplayMessage
    def self.message(message)
        puts "Received at #{Time.now.strftime('%I:%M:%S %p')} and message is #{message}"
        ## Intentionally added sleep to test whether Celluloid block the main process for 60 seconds or not.
        if message == 'client-1'
           puts 'Going to sleep now'.red
           sleep 60
        end
    end
end

server = Server.new()
server.async.run
sleep