For one of the pet projects I'm working on, I really want to create a push notification system. The site itself is written with PHP using the Kohana Framework. This works great and was a super fast and easy way to get things up and running. However, as I found out, this system isn't really conducive to the "push" notification system I wanted. I originally went with the tried & true method of long polling. Using an PHP/AJAX example I found, I got it working. But I knew this wasn't really the ideal solution.
I did more searching around, and was reading about Web Sockets that are part of the HTML 5 spec. I eventually came across the node.js plugin Socket.IO. Now I was already using PHP and Apache for my web application, so I didn't want to have to redo it all to be a node.js website. So instead, I set out to create "relay" system that clients could subscribe to and my PHP scripts could send notifications too. After playing around, it wasn't too difficult to get working.