When you say plugin, what do you exactly mean by that?
Do you mean plugins for IDEs that are available at the development time. Or it is kind of a framework for some specific functionality which you use of Rails. Like we have hibernate framework in Java for ORM etc.
BTW, what IDE is used for Ruby/Rails developement.
Plugins are "libraries" which provide functionality to a rails application. They could add functionality to models, such as acts_as_list or to controllers or views. Generally they are small pieces of code which do one thing, although some are large and provide much more functionality.
Well... Not really. Those would be more like rubygems. The plugins are more application specific (i.e. rails specific) and provide code for the rails environment -- like a forms helper plugin, or something which allows for tagging of posts.