Scott Raymond has written a useful article showing the thinking behind his refactoring of IconBuffet.com from an action-heavy URL scheme to a REST based URL scheme.
The application behind IconBuffet.com, a royalty-free stock icon store, went from 10 controllers and 76 actions to 13 controllers that more closely followed the models involved, and 58 total actions. Most of the new actions are uniform and match to the new Rails methodology of mapping HTTP verbs (GET, PUT, POST, DELETE, etc.) to Rails controller actions. You can learn more about this structure from David Heinemeier Hansson's slides (PDF) from RailsConf, or watch the video of his keynote presentation.

Alex MacCraw has been working on a great plugin called Juggernaut, and has now made his first public release:

This one is for Mac users only..

Bruce Williams tries to solve the problem of multiple parameter types in Rails. For example, an action may accept dates via a parameter, but dates may be supplied in many forms. A 'date' parameter might arrived as if from a date_select helper, or might even be typed in directly by a user, or be pulled from a database. Rather than use before_filters to check parameters and normalize them, Bruce suggests that it should be possible to add basic conversion tools to certain data types so that all data is normalized by the time it hits your controllers.

In the recent 19 Rails Tricks Most Rails Coders Don't Know article, I recommended the use and development of engines to implement common functionality in Rails applications. I simply provided a link to the Rails Engines site and left it at that.

Active Merchant is a payment processing library for Rails developed by the geniuses behind Rails powered e-commerce system, Shopify. It's under active development with support for different payment processor gateways being added regularly. So far it supports:

There are many scenarios where you might want the same controller action / method in your Rails application to perform multiple functions. For example, a wizard with multiple steps or a single form with multiple-stage AJAX calls. What you want to do is provide a 'context' to the specific request and have the controller handle that in some different way.

Action Messenger, by Trejkaz Xaoza, is a basic wrapper around Ruby's xmpp4r Jabber library that makes Jabber instant messaging services directly available to Rails applications. (Jabber is an open, XML specification and framework for instant messaging. Google Talk uses it, for example.)