ripl is a light shell that encourages common middleware for shells i.e. rack for ruby shells. It is also a modular alternative to irb. Like irb, it loads ~/.irbrc, has autocompletion and keeps history in ~/.irb_history. Unlike irb, it is highly customizable via plugins and supports commands i.e. ripl-play. This customizability makes it easy to build custom shells (i.e. for a gem or application) and complex shells (i.e. for the web). Works on ruby 1.8.7 and greater.
Gemfile gem 'ripl', '~> 0.7.1'
install gem install ripl