Ruby on Rails is an open source web application development framework that has been written in Ruby language. Ruby on Rails has become very popular due to its rapid development environment.

Ruby on Rails is based on Model-View-Controller design paradigm. RoR follow two important design principals 

• Convention over Configuration (CoC)

• Don't Repeat Yourself (DRY)

Check out rubyonrails.org for more information

Example of some Ruby on Rails web applications

There are many high profile websites developed using Ruby on Rails. For example

• BBC Programme Catalogue – video and audio archives from BBC television and radio
• Justin.tv - A live video streaming platform
• OpenCongress – Aggregated news and official data about the US Congress
• yellowpages.com – US telephone directory