As web based collaboration apps become more accepted and used it's forcing developers to clients and servers in sync in near real-time. Tools and frameworks that make it easier to keep all instances for a client in sync are very helpful, because it can be kind of tricky from a development perspective.

Juggernaut is one such framework. It's for Rails and uses sockets trough the flash player to push data from the server to the client. It's end result is similar to Comet or Reverse Ajax. The key difference is that it uses the Flash Player to do the data transport, very cool!

"The Juggernaut plugin for Ruby on Rails aims to revolutionize your Rails app by letting the server initiate a connection and push data to the client. In other words your app can have a real time connection to the server with the advantage of instant updates. Although the obvious use of this is for chat, the most exciting prospect is collaborative cms and wikis."

Here's a diagram of how Juggernaut works:

I'm of the opinion that polling is often good enough. This is where some client code polls the server every so often to check for updates. At the same time I like my Blackberry better than my iPhone because email is instantly pushed to it, I don't have to check. Using push is higher performance and uses less server resources, so given it's easy enough to do it's probably worth it.