title: Best way to implement a push notification systems
body: <p>We would like to make a realtime price change system to be able to see difference with competitor prices against our product prices.</p>
  
  <p>We have no experience with Push notification / COMET system by Javascript and PHP. If you don't mind, I would like to get your experiences, suggestions about this technique. So here are my questions:</p>
  
  <ul>
  <li>What is the best way doing like that system?</li>
  <li>We are experienced PHP developers, so is PHP appropiate for this task? </li>
  <li>If you know any project or solution ( open source or commercial ) that is able to do this, could you please share?</li>
  </ul>