ruby Push Engine

1.The github repository : https://github.com/maccman/juggernaut Example of application with juggernaut :https://github.com/maccman/holla

2.

Check out Faye: http://faye.jcoglan.com/ - I hear really good things about it.

if you're looking for a hosted solution, i've used Pusher http://pusher.com/ in the past, and loved it. i converted a site that used ajax polling over to pusher in about 30 minutes.

3.ajax engine