client.rb

require 'socket'

while line = gets
  s = TCPSocket.open('127.0.0.1', 2000)
  s.puts line.chop
  puts s.gets
  s.close
end

server.rb

require 'socket'
require 'thread'

server = TCPServer.open(2000)
messages = Queue.new
clients = []

while true
  Thread.start do
    loop do
      while message = messages.pop do
        clients.each do |client|
          client.print message
        end
      end
    end

    loop do
      Thread.new(server.accept) do |s|
        clients << s
        messages << s.gets
      end
    end
  end
end