Push technologies - Comet server

CometD is based on Ajax Push technology pattern known as Comet. Alex Russel first mentioned about this in his post Comet: Low Latency Data for the Browser

 There are today a list of Comet frameworks or implementations that we can use:

1. http://www.stream-hub.com - There is a free community edition. But I think this is better to invest time and money in a fully open source framework.
2. http://www.frozenmountain.com/websync/ -commercial. Not to recommend. You won't want to invest money and time in a framwork that you do not know how long they will last.
3. http://orbited.org - seems good. Worth to give a try.
4. https://github.com/Atmosphere/atmosphere - Seems far better than frameworks. This supports sramework like Jersey, GWT, Wicket, Vaadin, Guice, Spring, JSF, Scalatra, Grails etc. You can use Scala, JRuby, Groovy and Java to write Atmosphere application. Mssive scalability with our Cluster plugin architecture (JGroups, JMS/ActiveMQ, Redis, XMPP, etc.) without paying one pence for it!
5. http://cometd.org/ - CometD Project of The Dojo Foundation. An implementation of Bayeux Protocol