ruby-growl is a platform-independent Ruby library for sending Growl 
notifications.

Growl (http://growl.info) is a really cool notification system for Mac 
OS X.

You can get the full scoop on ruby-growl here:

http://segment7.net/projects/ruby/growl/

You can download ruby-growl as a gem:

http://segment7.net/projects/ruby/growl/ruby-growl-1.0.0.gem

Or as a .tgz:

http://segment7.net/projects/ruby/growl/ruby-growl-1.0.0.tgz