Cacophony is a small program that broadcasts notifications via a variety of mechanisms, such as growl, email and twitter. It is great for notifiying you(or others) when a long running task is complete. It operates as a standalone executable, and it also can read from STDIN to pipe output from your tasks to the notifiers.
Gemfile gem 'cacophony', '~> 0.0.3'
install gem install cacophony -v 0.0.3