A very simple Ruby Interpreter Online, based on Sinatra
bundle install
ruby onlineirb.rb
Then you would be able to access localhost:4567 from your browser.
You can clear the console by:
irb> clear
You also can use ending \ to continue programming, the whole bunch of code would be executed at the statement without \ ending.
You can also deploy this project to cloudfoundy.com without any changes required.