Ruby on Rails is separated into various packages, namely ActiveRecord, ActiveResource, ActionPack, ActiveSupport and ActionMailer. Prior to version 2.0, Ruby on Rails also included the Action Web Service package that is now replaced by Active Resource.
Apart from standard packages, developers can make plugins to extend existing packages. Rails 3.2 deprecates the old plugins Rails 2-3-stable style in which plugins are to be placed under vendor/plugins, in favor of packaged gems.
First of all, Ruby on Rails is 100% open-source, available under the permissive MIT License, and as a result it also costs nothing to download or use. Rails also owes much of its success to its elegant and compact design; by exploiting the malleability of the underlying Ruby language, Rails effectively creates a domain-specific language for writing web applications. As a result, many common web programming tasks—such as generating HTML, making data models, and routing URIs—are easy with Rails, and the resulting application code is concise and readable.
Rails also adapts rapidly to new application development in web technology and framework design. For example, Rails was one of the first frameworks to fully digest and implement the REST architectural style for structuring web applications.
Tens of thousands of Rails applications are already live. People are using Rails in the tiniest part-time operations to the biggest companies.