chat_client.rb

require 'socket'

host = 'their.ip.address'
port = 33_333

udpsock = UDPSocket.new
udpsock.setsockopt(Socket::SOL_SOCKET, Socket::SO_BROADCAST, true)

loop do
  data = gets.chomp
  udpsock.send(data, 0, host, port)
  break if data == '/quit'
end

udpsock.close

chat_server.rb

require 'socket'

host = 'your.IP.address'
port = 33_333
BasicSocket.do_not_reverse_lookup = true

udpsock = UDPSocket.new
udpsock.bind(host, port)

loop do
  data, _ = udpsock.recvfrom(1024)
  puts data
  break if data == '/quit'
end

udpsock.close